Electronic device and method of manufacturing the same

ABSTRACT

In the present invention, an etching hole  21  is formed in a polysilicon film  14  as a cavity-wall member. Through the etching hole  21,  hydrofluoric acid is injected, so as to dissolve a silicon oxide film  13,  thereby forming a cavity  22.  In the cavity  22,  a detecting unit  12  of a sensor is in an exposed condition. Next, by sputtering, an Al film  16  is deposited in the etching hole  21  and on an upper face of a substrate. Thereafter, a portion of the Al film  16  positioned on the polysilicon film  14  is removed by etching back, thereby leaving only a metal closure  16   a  of Al which closes the etching hole. The sputtering step is performed under a pressure of 5 Pa or less, so that the pressure in the cavity can be held to be low.

TECHNICAL FIELD

The present invention relates to an electronic device provided with acavity of which an internal pressure is held at a low level and aproduction method thereof. The present invention particularly relates toan electronic device in which a sensing unit of an infrared sensor orthe like is hermetically closed in an atmosphere of a reduced pressure,and a production method thereof. In addition, the present inventionrelates to an electronic device in which a pressure of the atmosphere insuch a cavity can be measured, and the pressure can be further reducedas required, and a production method thereof.

BACKGROUND ART

For the purpose of increasing detection sensitivity, in an electronicdevice such as an infrared sensor, conventionally, at least a sensingunit is disposed in a cavity formed on a substrate, and the sensing unitis hermitically closed in a vacuum atmosphere or an inert gas atmosphereby a cap unit.

Such electronic devices include, other than the infrared sensor, apressure sensor, an acceleration sensor, a flow-rate sensor, a vacuumtransistor, and the like.

Among such sensors, infrared sensors can be generally classified intothermal sensors such as a bolometer sensor, a pyroelectric sensor, athermopile sensor, or a thermocouple sensor, and quantum-type sensorsusing PbS, InSb, HgCdTe, or the like. Many of the bolometer sensorscomprise detecting units formed from a resistivity-changeable materialsuch as polysilicon, Ti, TiON, or VO_(x), but some utilize a transientcharacteristic of a forward current of a PN diode, or the like. Thethermopile sensor utilizes Seebeck effect caused in a PN junction, forexample, and the pyroelectric infrared sensor utilizes the pyroelectriceffect of a material such as PZT, BST, ZnO, or PbTiO₃. The quantumsensor detects a current caused by electronic excitation. In addition,there is an infrared sensor having chromel-alumel thermocouple whichdetects infrared rays by Seebeck effect, or the like.

In order to maintain the detection sensitivity and the accuracy of theinfrared sensor at high levels, it is preferred that heat dissipationfrom an infrared detecting unit be as small as possible. It is knownthat when the detecting unit is enclosed in a vacuum atmosphere or aninert gas atmosphere of a reduced pressure which is hermetically sealedby a micro vacuum package, or the like, the detection characteristicsare improved.

The sensitivity of the pressure sensor or the acceleration sensor isalso improved when the viscous resistance of the air existing around thedetecting unit is lowered, so that it is preferred that the detectingunit be enclosed in a vacuum atmosphere or an inert gas atmosphere of areduced pressure which is hermetically sealed by a cap unit, or thelike. When the interior of the cap unit is sealed so as to be in avacuum condition, preferably, it can be confirmed that the vacuum levelin the cap unit can be held in the production or in the use of theelectronic device.

Hereinafter with reference to FIGS. 1A to 1F, a conventional method offabricating an electronic device will be described.

In a step shown in FIG. 1A, a silicon substrate 101 on which a sensingunit 102 of an infrared sensor or the like is formed is prepared. Aftera silicon oxide film 103 is deposited on the substrate by CVD, forexample, the silicon oxide film 103 is patterned so as to cover thesensing unit 102 and the peripheral portion thereof. Since the siliconoxide film 103 functions as a sacrificial layer, the silicon oxide filmis removed by etching in a succeeding step, thereby defining the shapeof a cavity.

In a step shown in FIG. 1B, a polysilicon film 104 is formed so as tocover the silicon oxide film 103 by CVD. The polysilicon film 104constitutes a sidewall and a ceiling wall of a cap unit of theelectronic device.

In a step shown in FIG. 1C, a number of etching holes 111 which runthrough the polysilicon film 104 and reach the silicon oxide film 103are formed.

In a step shown in FIG. 1D, hydrofluoric acid is injected through theetching holes 111, so as to dissolve the silicon oxide film 103. Thesolution is removed via the etching holes 111. As a result, a cavity 112surrounded by the silicon oxide film 103 is formed, and the sensing unit102 of the sensor is exposed in the cavity 112.

Next, in a step shown in FIG. 1E, a polysilicon film 106 is deposed byCVD so as to cover the polysilicon film 104. At this time, thepolysilicon film 106 is also deposited in interior walls of the etchingholes 111, so as to close the etching holes 111. In a time period afterthe start of CVD until the etching holes are completely closed, thepolysilicon film 106 is deposited on an interior wall of the cavity 112.

The above-mentioned CVD process is generally performed by using areaction gas such as SiH₄ under a pressure of 500 mTorr (about 67 Pa).Therefore, the cavity 112 is hermetically sealed in a condition wherethe internal pressure is about 500 mTorr (about 67 Pa) in the CVDprocess. In addition, in the CVD process, SiH₄ which is not yet reactedand an H₂ gas caused by the reaction remain in the interior of thecavity 112. Moreover, SiH₄ which is not yet reacted and the H₂ gascaused by the reaction are adsorbed to the polysilicon film 106deposited on the wall of the cavity 112.

Next, in a step shown in FIG. 1F, the whole of the substrate 101 isheated at high temperatures of 500° C. or more under high vacuum. Atthis time, the SiH₄ gas in the cavity 112 is decomposed to some extent,and the H₂ gas is discharged to the exterior through the polysiliconfilms 104 and 106. Accordingly, the pressure in the cavity 112 isslightly reduced from the internal pressure of the cavity 112 in the CVDprocess, so that the vacuum level of the cavity 112 is somewhatincreased.

The above-described production method is described in Japanese Laid-OpenPatent Publication No. 2000-124469, for example.

Next, a prior art for increasing the vacuum level in the interior of avacuum package (a cap unit), and a prior art for measuring a vacuumlevel (a pressure) will be described.

FIG. 42 schematically shows a sectional configuration of an electronicdevice having a conventional vacuum package (see Japanese Laid-OpenPatent Publication No. 11-326037). The electronic device shown in FIG.42 includes a silicon substrate 91, a transmitting window 94 fixed onthe silicon substrate 91 by means of a solder 99. A gap 93 having aheight of about 1 to 10 mm is disposed between the transmitting window94 and the silicon substrate 91. A getter 95 having a size of severalmillimeters is disposed in the gap 93.

A through hole 97 is formed in the transmitting window 94, and thegetter 95 is disposed in the gap 93 through the through hole 97. Whenthe silicon substrate 91 is disposed in a vacuum, the gap 93 isevacuated through the through hole 97, so that the pressure is reduced.The through hole 97 is closed by melting the solder 99 for vacuumsealing, so as to hold the gap 93 in a vacuum condition. Thereafter,when the getter 95 is activated, the pressure of the gap 93 is furtherreduced, and a high vacuum condition can be attained.

The vacuum level in the cap unit can be measured by using a Piranigauge, for example. The Pirani gauge is an apparatus for obtaining avacuum level based on an electric resistance value of the resistiveelement disposed in a vacuum. The coefficient of thermal conductivity ofa gas depends on a pressure of the gas, i.e., a vacuum level. For thisreason, if the coefficient of thermal conductivity from a heatedresistive element to the gas is obtained, it is possible to determinethe vacuum level of the gas by appropriate calibration.

Recently, electronic devices are miniaturized, so that theabove-described vacuum packages (cap units) are more strongly requiredto be microminiaturized. For example, an image sensor in which a numberof infrared detecting units and visible-light detecting units arrangedin a matrix are provided on one and the same substrate is proposed. Insuch an image sensor, each of the infrared detecting units having a sizeof about 50 μm×50 μm is sealed by a micro vacuum package having a sizeof about 100 μm×100 μm (Japanese Laid-Open Patent Publication No.2003-17672).

In order to manufacture a microminiaturized electronic device on whichan FEA device and a transistor for performing high-speed switchingoperation in a vacuum are mixedly mounted, a technique in which amicrominiaturized vacuum package is formed only in a portion of the FEAdevice on the substrate is described, for example, in Siliconmetal-oxide-semiconductor field effect transistor/field emission arrayfabricated using chemical mechanical polishing, C. Y. Hong and A. I.Akin-wande, J. Vac. Sci. Technol. B Vol. 21, No. 1, p 500-505,January/February 2003.

According to the above-described method of fabricating the electronicdevice, the SiH₄ gas is decomposed in the cavity 112 in the thermaltreatment step shown in FIG. 1F, and the H₂ gas is discharged to theexterior of the cavity 112. Therefore, the vacuum level in the cavity isslightly increased as compared with the pressure of 500 mTorr (about 67Pa) in the CVD process. However, there exists a problem that an increasein vacuum level is not expected, for the purpose of improving thesensitivity of the sensor.

In the above-described production method, any cavity is not formedbetween the detecting unit 102 and the substrate 101. By disposingsacrificial layers for respective upper and lower layers of thedetecting unit 102, it is possible to fabricate a configuration in whichthe atmospheric gas in the cavity is in contact not only above but alsobelow the detecting unit 102.

FIG. 2 is a perspective view showing the vicinity of a detecting unit ofa bolometer-type infrared sensor having such a configuration. In FIG. 2,a resistive element 151 referred to as a “bolometer” functioning as aninfrared detecting unit, and a supporting member 152 for supporting theresistive element 151 are formed on a substrate 101. The resistiveelement 151 is formed from a patterned polysilicon film, for example.The supporting member 152 is often disposed by laminating a polysiliconfilm, a nitride film, an oxide film, and the like. The supporting member152 has arm portions extended from a supporting main portion on an upperface of which the resistive element 151 is formed. The supporting member152 is fixed to the substrate 101 via the arm portions.

In FIG. 2, a cavity-wall member is not shown. In an actual infraredsensor, a supporting member 150 is disposed in an interior of a cavitywhich is the same as the cavity 112 shown in FIG. 1F.

Hereinafter, a problem caused in the case where the etching holes areclosed by CVD will be described in detail.

Although not shown in FIG. 2, when infrared rays pass through thepolysilicon films surrounding the cavity (the films indicated by thereference numerals 104 and 106 in FIG. 1F) and are incident on theresistive element 151, the temperature of the resistive element 151 isincreased. In conjunction with the temperature rise, the resistancevalue is varied. The infrared sensor having the configuration of FIG. 2measures the change of the resistance value, so as to detect the amountof infrared rays incident on the resistive element 151.

In order to increase the detection sensitivity of the infrared sensor,it is necessary to increase the magnitude of temperature rise of theresistive element 151 when the infrared rays are incident on theresistive element 151. Therefore, it is preferred that the resistiveelement 151 functioning as an infrared detecting unit and the exteriorthereof be thermally insulated as much as possible.

The thermal conductance between the resistive element 151 and theexterior thereof is classified into thermal conductance via thesupporting member 152 which connects the resistive element 151 to thesubstrate 101, and thermal conductance via a gas around the resistiveelement 151.

The thermal conductance via the supporting member 152 becomes smaller,as a sectional area of the narrowest portion of the supporting member152 is smaller, and as the distance from the substrate 101 is larger.For example, if a technique of MEMS (Micro-Electro-Mechanical Systems)is used, it is possible to configure the portion (the connectingportion) of the supporting member 152 coupled to the substrate 101 bytwo columns of Si₃N₄ having a sectional area of 3 μm² and a length of 50μm. In this case, the thermal conductance is 3×10⁻⁷ (W/K).

On the other hand, the thermal conductance via the gas around theresistive element 151 is smaller, as the pressure of the gas is smaller.For this reason, it is necessary to reduce the pressure of the gasaround the detecting unit, in order to increase the sensitivity of theinfrared sensor.

However, in the conventional production method described with referenceto FIGS. 1A to 1F, after the step shown in FIG. 1E, the internalpressure of the cavity 112 is maintained at about 500 mTorr (about 67Pa) by the residual gas. After the formation of the cavity 112, vacuumand high temperature treatment is performed, thereby diffusing hydrogenin the interior into the exterior. Thus, the internal pressure of thecavity 112 can be somewhat reduced, but the SiH₄ gas which cannot bedischarged to the exterior of the cavity 112 by the high temperatureheating remains in the cavity.

In the infrared image sensor such as a bolometer type, a relationshipshown in the graph of FIG. 3 exists between the pressure of the gascovering the detecting unit and the sensitivity. Such a relationship isdescribed, for example, in “Uncooled Infrared Imaging Arrays andSystems” by Academic Press, page 115.

In the graph of FIG. 3, the ordinate indicates the sensitivity, and theabscissa indicates the atmospheric pressure of the detecting unit 12. Asis seen from the graph, as the pressure is lower, the sensitivityincreases. The sensitivity in the case of the pressure of 50 mTorr isabout three times as much as the sensitivity in the case of the pressureof 500 mTorr. Therefore, it is desired that the internal pressure of thecavity is 50 mTorr or less.

The supporting member 152 for the detecting unit 151 of the infraredsensor has a minute configuration as shown in FIG. 2. Thus, if theheating at extremely high temperatures is performed in the step of FIG.1F, thermal stress is generated in the supporting member 152, so thatthe supporting member 152 may be broken.

In the case where high temperature heating of 660° C. or more isperformed, there arises a problem that Al used as wiring for the sensoris molten. Thus, it is necessary to perform the heating at thetemperature or lower temperatures. However, in such temperatures, thediffusion velocity of H₂ to the exterior is very low, so that thefunction as the heating for increasing the vacuum level is not expectedso much.

As described above, by the conventional production method in which theetching holes are closed by CVD, it is difficult that the vacuum levelof the cavity 112 is further increased, and hence the detectionsensitivity is increased.

If the method described with reference to FIG. 12 is adopted in order toincrease the vacuum level, it is extremely difficult to dispose thegetter shown in FIG. 12 in the minute cavity with good yield.

If the above-mentioned vacuum package (the cap unit) is miniaturized soas to have a size of 1 mm or less, it becomes further difficult todispose the getter agent in the interior of each vacuum package by aconventional method. For example, in the case where each of the infrareddetecting units is sealed by a micro vacuum package having a size ofabout 100 μm×100 μm, it is very difficult and it takes a lot of troubleto disposed a getter agent in the interior of each of a number of vacuumpackages.

Moreover, many of the techniques for detecting the vacuum level by aconventional Pirani gauge are produced for the purpose of measuring thevacuum level in a vacuum chamber of a large-size apparatus. Thus, thesmallest detecting device has a length of about 0.2 inches. Therefore,the conventional Pirani gauge is not suitable for measuring the internalpressure of the above-mentioned micro vacuum package.

The present invention has been conducted in view of the above-describedprior art, and it is an object of the present invention to provide anelectronic device at least part of which is held in a cavity, and aninternal pressure f the cavity can be reduced as compared with theconventional one, and to provide a production method thereof.

It is another object of the present invention to provide an electronicdevice which can measure an internal pressure of a micro vacuum package,and a production method thereof.

It is still another object of the present invention to provide anelectronic device in which the vacuum level in a micro vacuum packagecan be easily maintained or improved, and a production method thereof.

DISCLOSURE OF THE INVENTION

The method of fabricating an electronic device according to the presentinvention includes the steps of: (a) preparing a substrate on which partof the electronic device is disposed, and forming a sacrificial layerwhich covers the part of the electronic device on a selected region ofthe substrate; (b) forming a cavity-wall film which covers thesacrificial layer on the substrate; (c) forming at least one openingwhich runs through the cavity-wall film and reaches the sacrificiallayer in the cavity-wall film; (d) selectively etching at least part ofthe sacrificial layer via the opening, thereby forming a cavitysurrounding the part of the electronic device; and (e) forming a sealingmember for closing the opening by sputtering.

In a preferred embodiment, in the step (e), the sealing member is formedby sputtering a metal.

In a preferred embodiment, in the step (e), the sealing member is formedby sputtering silicon.

In a preferred embodiment, in the step (e), after a film for the sealingmember is deposited in the opening and on the cavity-wall film, aportion of the film for the sealing member positioned on an upper faceof the cavity-wall film is removed, thereby leaving the sealing memberin the opening.

In a preferred embodiment, in the step (e), the sputtering is performedin an inclined direction with respect to a direction perpendicular to amain face of the substrate.

In a preferred embodiment, in the step (c), an opening having a shapewhich is wider in an upper portion and is narrower in a lower portion isformed.

In a preferred embodiment, in the step (b), a side opening which reachesa side face of the sacrificial layer is additionally formed.

In a preferred embodiment, in the step (b), the opening is formed sothat the opening does not overlap the part of the electronic device asseen from the direction of the sputtering in the step (e).

In a preferred embodiment, in the step (e), the sputtering is performedunder a pressure of 10 Pa or less.

In a preferred embodiment, in the step (e), the sputtering is performedunder a pressure of 5 Pa or less.

In a preferred embodiment, in the step (a), the sacrificial layer isformed from a polysilicon film, and in the step (b), a silicon oxidefilm is formed as the cavity-wall film.

In a preferred embodiment, the part of the electronic device is adetecting unit of an infrared sensor, in the step (a), the sacrificiallayer is formed from a polysilicon film, and in the step (b), apolysilicon film and a silicon oxide film enwrapping the polysiliconfilm are formed as the cavity-wall film.

In a preferred embodiment, in the step (a), the sacrificial layer isformed from a silicon oxide film, and in the step (b), a polysiliconfilm is formed as the cavity-wall film.

In a preferred embodiment, the production method further includes thestep of, after the step (d) and before the step (e), depositing a filmon an exposed surface of the substrate by CVD, thereby making theopening smaller.

In a preferred embodiment, the production method further includes thestep of, before the step (a), forming a detecting unit of an infraredsensor as the part of the electronic device, and a sacrificial layer fora lower cavity embedding the side and the bottom side of the detectingunit, and in the step (d), the sacrificial layer and the sacrificiallayer for the lower cavity are removed.

The electronic device according to the present invention includes: asubstrate; part of the electronic device disposed on the substrate; acavity-wall member surrounding the part of the electronic device with acavity interposed therebetween; and a sealing member for closing anopening disposed in a ceiling portion of the cavity-wall member, and thesealing member is formed by sputtering.

In a preferred embodiment, the sealing member is constituted by silicon.

In a preferred embodiment, the sealing member is constituted by a metal.

In a preferred embodiment, a pressure in the cavity is 10 Pa or less.

In a preferred embodiment, a pressure of the cavity is 5 Pa or less.

In a preferred embodiment, the sealing member is constituted by a metal.

In a preferred embodiment, the sealing member is constituted by an oxidefilm.

In a preferred embodiment, the part of the electronic device is adetecting unit of an infrared sensor, and the cavity-wall member isconstituted by polysilicon and a silicon oxide film enwrapping thepolysilicon.

In a preferred embodiment, the part of the electronic device is adetecting unit of an infrared sensor, and the side and the bottom sideof the detecting unit are surrounded by a lower cavity.

In a preferred embodiment, the opening does not overlap the part of theelectronic device as seen from the direction of sputtering.

In another aspect of the present invention, the method of fabricating anelectronic device including a cavity of reduced pressure, and a pressuremeasuring element at least part of which is disposed in the cavityincludes the steps of: (a) disposing the pressure measuring element on asubstrate; and (b) forming the cavity so as to include the at least partof the pressure measuring element, wherein the step (b) of forming thecavity includes the step (b1) of forming an opening for supplying anetchant to a region to be etched, the step (b2) of supplying the etchantto the region to be etched through the opening, thereby removing theregion to be etched, and the step (b3) of forming a sealing member forclosing the opening by sputtering.

In a preferred embodiment, the step (a) includes the step (a1) offorming a heat absorbing and/or emitting portion having a function ofheat generation and/or heat sink and a temperature detecting portionhaving a function of detecting a temperature on the substrate by a thinfilm deposition technique, thereby forming the pressure detectingelement.

In a preferred embodiment, the heat absorbing and/or emitting portiongenerates heat by Joule heat.

In a preferred embodiment, the temperature detecting portion detects atemperature based on a resistance variation depending on a temperatureof an electric resistor.

In a preferred embodiment, the heat absorbing and/or emitting portionhas a function of generating heat by Joule heat by means of an electricresistor and a function of detecting a temperature based on a resistancevariation depending on a temperature of an electric resistance of theelectric resistor, and the heat absorbing and/or emitting portion andthe temperature detecting portion are constituted by one and the samethin film of an electric resistive element.

In a preferred embodiment, the heat absorbing and/or emitting portion isa Peltier element.

In a preferred embodiment, the step (b) includes: the step of forming asacrificial layer functioning as the region to be etched on the pressuremeasuring element; the step of forming a cavity-wall film which coversthe sacrificial layer on the substrate; and

the step of forming the opening in the cavity-wall film, therebyexposing at least part of the sacrificial layer via the opening.

In a preferred embodiment, the production method further includes thestep of, before the step (a1) is performed, forming a sacrificial layerfor thermally insulating the heat absorbing and/or emitting portionwhich covers part of the substrate on a selected region of thesubstrate, and the step of, after the step (a1) is performed, removingat least part of the sacrificial layer for thermally insulating the heatabsorbing and/or emitting portion.

In a preferred embodiment, the production method further includes: thestep of, before the step (a1) is performed, forming a sacrificial layerfor thermally insulating the heat absorbing and/or emitting portionfunctioning as part of the region to be etched on a selected region ofthe substrate; the step of, after the pressure measuring element isformed on the sacrificial layer for thermally insulating the heatabsorbing and/or emitting portion, forming a cavity-wall sacrificiallayer functioning as another part of the region to be etched on thepressure measuring element; the step of forming a cavity-wall filmcovering the sacrificial layer for thermally insulating the heatabsorbing and/or emitting portion and the cavity-wall sacrificial layer;the step of forming the opening in the cavity-wall film, therebyexposing a surface of a portion of at least one of the sacrificial layerfor thermally insulating the heat absorbing and/or emitting portion andthe cavity-wall sacrificial layer; and the step of removing at leastpart of the sacrificial layer for thermally insulating the heatabsorbing and/or emitting portion and the cavity-wall sacrificial layervia the opening.

In a preferred embodiment, the production method further includes: thestep of forming an etch stop layer on the substrate; the step of formingthe opening in the etch stop layer; the step of forming at least one ofthe heat absorbing and/or emitting portion and the temperature detectingportion on the etch stop layer; and the step of supplying the etchantthrough the opening, and removing a region of the substrate functioningas the region to be etched, thereby forming at least part of the cavity.

In a preferred embodiment, the production method further includes: thestep of preparing, as the substrate, a substrate having a regionfunctioning as an etch stop layer in the surface or in the insidethereof and having a region functioning as the region to be etched belowthe region functioning as the etch stop layer; the step of forming theopening in the etch stop layer;

the step of forming at least one of the heat absorbing and/or emittingportion and the temperature detecting portion on the etch stop layer;and the step of supplying the etchant via the opening and removing atleast part of the region to be etched of the substrate.

In a preferred embodiment, the heat absorbing and/or emitting portionhas a size of 1 mm or less.

In a preferred embodiment, the step (b3) is performed under a pressureof 10 Torr or less.

In a preferred embodiment, in the step (b3), silicon is sputtered.

In a preferred embodiment, the thin film deposition technique is vacuumevaporation.

In a preferred embodiment, the thin film deposition technique isperformed by CVD or PVD.

In a still another aspect of the present invention, the method offabricating an electronic device which includes a cavity of reducedpressure, a gettering thin film, disposed in the cavity, having afunction of adsorbing an ambient material, and an activating portionhaving a function of activating the gettering thin film by heatgeneration includes the steps of: (a) providing the activating portionand the gettering thin film on a substrate by thin film depositiontechnique; and (b) forming the cavity, wherein the step (b) of formingthe cavity includes the step (b1) of forming an opening through which anetchant is supplied to a region to be etched, the step (b2) of supplyingthe etchant to the region to be etched through the opening, therebyremoving the region to be etched, and the step (b3) of forming a sealingmember for closing the opening by sputtering.

In a preferred embodiment, the step (a) includes the step (a1) offorming the activating portion by a thin film deposition technique, andthe step (a2) of forming the gettering thin film in a position which isin contact with the activating portion by a thin film depositiontechnique.

In a preferred embodiment, the step (a) includes, before the steps (a1)and (a2) are performed, the step of forming a sacrificial layer for theactivating portion which covers part of the substrate on a region inwhich the activating portion is formed, and the step (b) includes thestep of removing at least part of the sacrificial layer for theactivating portion.

In a preferred embodiment, the production method further includes: thestep of forming an etch stop layer on the substrate; the step of formingthe opening in the etch stop layer; the step of forming at least one ofthe activating portion and the gettering thin film on the etch stoplayer; and the step of supplying the etchant through the opening andremoving a region of the substrate functioning as the region to beetched, thereby forming at least part of the cavity.

In a preferred embodiment, the production method further includes: thestep of preparing, as the substrate, a substrate having a regionfunctioning as an etch stop layer in the surface or in the insidethereof and a region functioning as the region to be etched below theregion functioning as the etch stop layer; the step of forming theopening in the etch stop layer; the step of forming at least one of theactivating portion and the gettering thin film above the etch stoplayer; and the step of supplying the etchant through the opening,thereby removing at least part of the region to be etched of thesubstrate.

In a preferred embodiment, the step (b) includes the step of forming acavity-wall sacrificial layer functioning as the region to be etched onthe activating portion, the step of forming a cavity-wall film whichcovers the cavity-wall sacrificial layer on the substrate, and the stepof forming the opening in the cavity-wall film and exposing at leastpart of the cavity-wall sacrificial layer via the opening.

In a preferred embodiment, the activating portion has a size of 1 mm orless.

In a preferred embodiment, the step (b3) is performed under a pressureof 10 Torr or less.

In a preferred embodiment, in the step (b3), silicon is sputtered.

In a preferred embodiment, the thin film deposition technique is vacuumevaporation.

In a preferred embodiment, the activating portion generates heat due toJoule heat by an electric resistor.

In a preferred embodiment, the activating portion is a Peltier element.

In a preferred embodiment, the electronic device includes at least oneinfrared detecting portion and at least one visible-light detectingportion formed on the substrate, the cavity has a shape which surroundsat least part of the infrared detecting portion, but does not surroundpart of the visible-light detecting portion.

In a preferred embodiment, the number of the visible-light detectingportions formed on the substrate is plural, and the visible-lightdetecting portions are arranged on the substrate.

In a preferred embodiment, the numbers of the infrared detectingportions and the visible-light detecting portions formed on thesubstrate are plural, respectively, and the infrared detecting portionsand the visible-light detecting portions are arranged on the substrate.

The production method further includes the step of forming a mirror forreflecting infrared rays and visible light.

In another aspect of the present invention, the electronic deviceincludes: a substrate; part of the electronic device disposed on thesubstrate; a cavity-wall member surrounding the part of the electronicdevice with a cavity interposed therebetween; and a sealing member forclosing an opening disposed in a ceiling portion of the cavity-wallmember, wherein the sealing member is formed from a thin film, and aninternal pressure of the cavity is 10 Pa or less.

In a preferred embodiment, a gettering thin film is disposed inside thecavity.

In a preferred embodiment, at least part of the cavity exists below thegettering thin film.

In a preferred embodiment, the electronic device includes a micro heaterfor heating the gettering thin film.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a sectional view of a step illustrating a conventional methodof fabricating an electronic device.

FIG. 1B is a sectional view of a step illustrating the conventionalmethod of fabricating an electronic device.

FIG. 1C is a sectional view of a step illustrating the conventionalmethod of fabricating an electronic device.

FIG. 1D is a sectional view of a step illustrating the conventionalmethod of fabricating an electronic device.

FIG. 1E is a sectional view of a step illustrating the conventionalmethod of fabricating an electronic device.

FIG. 1F is a sectional view of a step illustrating the conventionalmethod of fabricating an electronic device.

FIG. 2 is a perspective view illustrating a configuration in thevicinity of a detecting unit of a bolometer-type infrared sensor.

FIG. 3 is a graph showing a relationship between an atmospheric pressureand sensitivity in a detecting unit of an infrared image sensor.

FIG. 4A is a sectional view showing a step before an etching opening isformed in a production process of an electronic device according to afirst embodiment of the present invention.

FIG. 4B is a sectional view showing a step before the etching opening isformed in the production process of the electronic device according tothe first embodiment of the present invention.

FIG. 4C is a sectional view showing a step before the etching opening isformed in the production process of the electronic device according tothe first embodiment of the present invention.

FIG. 4D is a sectional view showing a step after the etching opening isformed in the production process of the electronic device according tothe first embodiment of the present invention.

FIG. 4E is a sectional view showing a step after the etching opening isformed in the production process of the electronic device according tothe first embodiment of the present invention.

FIG. 4F is a sectional view showing a step after the etching opening isformed in the production process of the electronic device according tothe first embodiment of the present invention.

FIGS. 5(a) and 5(b) are fragmentary sectional views each of which showspart of a production process of an electronic device according to asecond embodiment.

FIG. 6 is a fragmentary cross-sectional view showing a configuration ofthe interior of a cavity of the electronic device in the secondembodiment in the case where first means for preventing the sensitivityof an infrared sensor from being deteriorated is provided.

FIG. 7A is a sectional view showing a step before a sacrificial layer isformed in a production process of an electronic device in a thirdembodiment of the present invention.

FIG. 7B is a sectional view showing a step before the sacrificial layeris formed in the production process of the electronic device in thethird embodiment of the present invention.

FIG. 7C is a sectional view showing a step before the sacrificial layeris formed in the production process of the electronic device in thethird embodiment of the present invention.

FIG. 7D is a sectional view showing a step before planarization of aBPSG film is performed after the sacrificial layer is formed in theproduction process of the electronic device in the third embodiment ofthe present invention.

FIG. 7E is a sectional view showing a step before planarization of theBPSG film is performed after the sacrificial layer is formed in theproduction process of the electronic device in the third embodiment ofthe present invention.

FIG. 7F is a sectional view showing a step before planarization of theBPSG film is performed after the sacrificial layer is formed in theproduction process of the electronic device in the third embodiment ofthe present invention.

FIG. 7G is a sectional view showing a step before patterning of aprotection film and the like is performed after the planarization of theBPSG film is performed in the production process of the electronicdevice in the third embodiment of the present invention.

FIG. 7H is a sectional view showing a step before patterning of theprotection film and the like is performed after the planarization of theBPSG film is performed in the production process of the electronicdevice in the third embodiment of the present invention.

FIG. 71 is a sectional view showing a step before patterning of theprotection film and the like is performed after the planarization of theBPSG film is performed in the production process of the electronicdevice in the third embodiment of the present invention.

FIG. 7J is a sectional view showing a step before an etching hole isformed after the patterning of the protection film and the like isperformed in the production process of the electronic device in thethird embodiment of the present invention.

FIG. 7K is a sectional view showing a step before the etching hole isformed after the patterning of the protection film and the like isperformed in the production process of the electronic device in thethird embodiment of the present invention.

FIG. 7L is a sectional view showing a step before the etching hole isformed after the patterning of the protection film and the like isperformed in the production process of the electronic device in thethird embodiment of the present invention.

FIG. 7M is a sectional view showing a step before a sealing member bywhich the etching hole is closed is formed after the etching hole isformed in the production process of the electronic device in the thirdembodiment of the present invention.

FIG. 7N is a sectional view showing a step before the sealing member bywhich the etching hole is closed is formed after the etching hole isformed in the production process of the electronic device in the thirdembodiment of the present invention.

FIG. 7O is a sectional view showing a step before the sealing member bywhich the etching hole is closed is formed after the etching hole isformed in the production process of the electronic device in the thirdembodiment of the present invention.

FIG. 8 is a planar layout view showing a groove 63 in FIG. 121.

FIG. 9 is a sectional view illustrating an infrared sensor according toa fourth embodiment of the present invention.

FIG. 10A is a sectional view of a step illustrating a method offabricating an electronic device according to a fifth embodiment of thepresent invention.

FIG. 10B is a sectional view of a step illustrating the method offabricating the electronic device according to the fifth embodiment ofthe present invention.

FIG. 10C is a sectional view of a step illustrating the method offabricating the electronic device according to the fifth embodiment ofthe present invention.

FIG. 11 is a sectional view illustrating a method of fabricating anelectronic device according to a sixth embodiment of the presentinvention.

FIG. 12(a) is a perspective view illustrating a seventh embodiment ofthe present invention, and FIG. 12(b) is an equivalent circuit diagramthereof.

FIG. 13 is a perspective view schematically showing a configuration ofan infrared detecting unit in the seventh embodiment of the presentinvention.

FIG. 14 is a plan view showing an exemplary layout of a micro heater167.

FIG. 15 is a perspective view showing an exemplary configuration of amicro heater supporting unit 168.

FIG. 16 is a perspective view showing an infrared detecting test unit.

FIG. 17A is a perspective view showing a configuration of a microheater.

FIG. 17B is a sectional view showing the configuration of the microheater (a sectional view taken across a bridge).

FIG. 17C is a sectional view showing the configuration of the microheater (a sectional view in parallel to a direction in which the bridgeextends).

FIG. 17D is a plan view showing the configuration of the micro heater.

FIG. 18 is a graph showing an exemplary relationship between an electricresistance and a vacuum level (a pressure) in the micro heater.

FIG. 19 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 20 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 21 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 22 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 23 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 24 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 25 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 26 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 27 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 28 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 29 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 30 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 31 is views showing a production step of the electronic device inthe seventh embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 32 is sectional views showing an electronic device in an eighthembodiment of the present invention in which (a) is a sectional viewtaken along a line A-A′, and (b) is a sectional view taken along a lineB-B′.

FIG. 33 is views showing a production step of the electronic device inthe eighth embodiment of the present invention in which (a) is asectional view taken along a line A-A′, (b) is a sectional view takenalong a line B-B′, and (c) is a plan view.

FIG. 34 is a view showing a ninth embodiment of the present invention.

FIG. 35 is an equivalent circuit diagram of the ninth embodiment of thepresent invention.

FIG. 36 is a graph showing a relationship between the sensitivity of theinfrared detecting unit and the vacuum level of the atmosphere.

FIG. 37 is a perspective view for illustrating coming and exiting ofheat in a resistive element.

FIG. 38 is a graph showing a temperature change of the resistive elementafter the resistive element is self-heated and left for a predeterminedperiod of time in which Pro1 to 3 indicate temperature profiles ofdevices 1 to 3 located in micro packages of different vacuum levels,respectively.

FIG. 39 is a timing chart for temperature measuring of the resistiveelement in the embodiment in which the abscissa indicates a time and theordinate indicates a driving voltage.

FIG. 40 is a diagram showing a circuit for processing an output signalof the infrared detecting unit and for complementing a defect inmeasuring a temperature for the purpose of determining the vacuum level.

FIG. 41 is a diagram schematically showing the arrangement of the microvacuum package in the cell array shown in FIG. 35.

FIG. 42 is a diagram schematically showing a sectional configuration ofan electronic device having a conventional vacuum package.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings.

EMBODIMENT 1

Hereinafter a first embodiment of the present invention will bedescribed with reference to the drawings.

First, in a step shown in FIG. 4A, a detecting unit 12 such as abolometer of an infrared sensor is formed on a main face of a siliconsubstrate 11. Specifically, after a thin film of a material having asensor function is deposited on the silicon substrate 11,micro-fabrication such as photolithography and etching is performed,thereby patterning the thin film. A planar shape of the detecting unit12 is designed so as to have the same planar shape as that of theresistive element 151 shown in FIG. 2, for example.

Next, after a silicon oxide film 13 which covers the detecting unit 12is deposited on the silicon substrate 11 by a thin film depositiontechnique such as CVD, the silicon oxide film 13 is patterned so as tocover the detecting unit 12 and the peripheral portion thereof. Thepatterning can be also performed by photolithography and etchingtechniques. The patterned silicon oxide film 13 functions as asacrificial layer, and is removed by etching later, thereby defining theshape of a cavity. The thickness of the silicon oxide film 13 definesthe height of the cavity. In this embodiment, the thickness of thesilicon oxide film 13 is set in the range of not less than 0.5 μm normore than 2 μm, for example.

Next, in a step shown in FIG. 4B, a polysilicon film 14 which covers thesilicon oxide film 13 is deposited on the silicon substrate 11 by thethin film deposition technique such as CVD. The polysilicon film 14 is acavity-wall member functioning as a sidewall and a ceiling wall of a capunit of the electronic device, after the cavity is formed. The thicknessof the polysilicon film 14 is set in the range of not less than 0.5 μmnor more than 2 μm, for example. In this embodiment, the sacrificiallayer which is removed by etching is formed from the silicon oxide film,so that it is necessary to form the cavity-wall member from a materialwhich is difficult to be etched by an etchant for etching the siliconoxide film. Polysilicon is one of materials exhibiting superioranti-etching property against various etchants utilized for etchingsilicon oxide.

In a step shown in FIG. 4C, a number of etching holes 21 which runthrough the polysilicon film 14 and reach the silicon oxide film 13 areformed. An arbitrary number of etching holes 21 are formed in arbitrarypositions and in an arbitrary arrangement by photolithography andetching techniques. In this embodiment, the diameter of the etching hole21 is set in the range of not less than 0.1 μm nor more than 6 μm.

Next, in a step shown in FIG. 4D, hydrofluoric acid is injected into theetching holes 21, so as to etch the silicon oxide film 13. The siliconoxide film 13 which is reacted with the hydrofluoric acid and dissolvedis removed via the etching holes 21, so as to form a cavity 22surrounded by the polysilicon film 14. In the interior of the cavity 22,the detecting unit 12 of the sensor is exposed.

In a step shown in FIG. 4E, an Al film 16 which covers an upper face ofthe polysilicon film 14 is formed on the silicon substrate 11. In thisembodiment, the Al film 16 is formed by sputtering in an obliquedirection. The thickness of the Al film 16 is varied depending on adiameter of the etching hole 21. In this embodiment, the thickness isset to be 2.0 μm. The sputtering is performed under a pressure of 5 Paor less. The etching holes 21 are closed by the Al film 16 and thepressure of the interior of the cavity is 5 Pa or less.

Next, as shown in FIG. 4F, portions of the Al film 16 which are higherthan the upper face of the polysilicon film 14 are removed byetching-back, and only a metal sealing member 16 a of Al which closesthe etching holes 21 is left. Herein, in the case where a relativelylarge detecting unit is disposed in the interior of the cavity 22, it ispreferred that the following steps A and B be performed before the stepshown in FIG. 4A, thereby depositing a sacrificial layer (the siliconoxide film 13) so as to cover the detecting unit of the sensor in a stepshown in FIG. AA.

Step A: Forming a detecting unit and a peripheral circuit portion of asensor

Step B: Forming a polysilicon film for covering the detecting unit andthe peripheral circuit portion of the sensor

Infrared rays can pass through the polysilicon film 14, but cannot passthrough the metal sealing member 16 a. However, the whole of the metalsealing member 16 a occupies an extremely small area, so that there isalmost no problem in actuality. As described later, the positions inwhich the etching holes 21 are formed in the step shown in FIG. 4E donot overlap the detecting unit (the resistive element 151 shown in FIG.2) of the infrared sensor as much as possible. Thus, it is possible tosuppress the deterioration in detection sensitivity for the infraredrays.

According to this embodiment, in the step shown in FIG. 4E, the Al film(the metal film) for closing the etching holes 21 is deposited bysputtering, so that it is possible to close the etching holes 21 under alower pressure as compared with the case of CVD (i.e., at a highervacuum level). Therefore, it is possible to hold the vacuum level of thecavity 22 high, and to hold the pressure to be 5 Pa or less, forexample. Therefore, the heat conductance from the detecting unit of thesensor disposed in the cavity 22 via the surrounding space can bereduced, and the detection sensitivity of the sensor can be improved.

According to this embodiment, it is unnecessary to perform thermaltreatment after the etching holes 21 are closed. Thus, it is possible toimprove the sensitivity of the sensor, without badly affecting aluminumwirings or the like. In addition, in this embodiment, since a metal isused for closing the etching holes 21, there exists almost nopolysilicon film which adsorbs a gas or the like in the cavity 22 as inthe case of CVD. Therefore, there does not occur such a problem that theresidual gas or the like is discharged into the cavity 22 during the useof the electronic device, so as to deteriorate the vacuum level.

In a step shown in FIG. 4F, it is desired that the sputtering beperformed in such a condition that an Ar gas is caused to flow into achamber at a flow rate of 10 to 30 (ml/min), and the temperature in thechamber is held at 400° C. to 500° C. If the temperature in the chamberduring the sputtering is lower than 400° C., the velocity of reflow ofsputtered Al particles is lowered. Thus, there occurs a portion in whichthe growth rate of the Al film is low. Thus, an extremely long time isrequired for closing the etching holes. On the other hand, thetemperatures exceeding 500° C. during the sputtering badly affect the Alwirings and the like.

In the case where the sputtering in the oblique direction is notperformed, it is desired that the distance between a target forsputtering and the substrate is 10 cm or less. In long-throw sputteringin which the distance between the target for sputtering and thesubstrate is 10 cm or more, a ratio of metal particles which arevertically incident on the upper face of the substrate is increased.Thus, the rate at which the metal film is deposited on a sidewallsurface of the etching hole is lowered. Therefore, a longer time isrequired for closing the etching holes, and the number of metalparticles invaded in the cavity is increased.

For example, in the case where the Ar gas is caused to flow into thechamber at a flow rate of 10 to 30 (ml/min), the temperature in thechamber is held at 400° C. to 500° C., and the distance between thetarget for sputtering and the substrate is 10 cm or less, a metal filmof about 600 nm is deposited on the upper face of the substrate forabout 40 seconds unless the sputtering in the oblique direction isperformed. At the same time, the etching holes each having a diameter of0.3 μm are closed.

The metals to be sputtered include, in addition to aluminum (Al),tungsten (W), titan (Ti), molybdenum (Mo), copper (Cu), tantalum (Ta),barium (Ba), strontium (Sr), platinum (Pt), rubidium (Rb), and the like,and compounds thereof. Any of the metals can be used.

In semiconductor process of the current 0.13 μm rule, in sputtering ofCu and Ta, the directivity is generally increased by generating plasmaat a pressure of several Pa and ionizing the sputtered metal. On theother hand, Al, Ti, and W are sputtered at a low pressure of about 100mPa. Therefore, in the case where the pressure in the chamber is desiredto be a low pressure of 10 mPa, it is preferred that the sputtering ofAl, Ti, and W be performed. In the case of a sensor requiring a vacuumwhich is not so high, such as an infrared sensor, it is preferred thatthe sputtering be performed at a pressure of 5 Pa or less. If thesputtering is performed at a pressure of 10 Pa or less, it is possibleto sufficiently improve the detection sensitivity of the sensor, ascompared with the conventional production method.

EMBODIMENT 2

Hereinafter a second embodiment according to the present invention willbe described.

In the above-described first embodiment, the etching holes 21 are closedby the metal sealing member 16 a by obliquely sputtering a metal fromthe above of the polysilicon film 14. Alternatively, instead of theoblique sputtering, if the shape of the etching hole 21 is contrived,the etching hole 21 can be closed by vertical sputtering.

FIGS. 5(a) and (b) are partial sectional views each showing part of aproduction process of an electronic device according to this embodiment.Both of FIGS. 5(a) and (b) show the configuration of the polysiliconfilm and the like formed in the step shown in FIG. 4E.

In the polysilicon film 14 of the electronic device according to amodification shown in FIG. 5(a), an etching hole 21 a of a tapered shapeis formed. In this modification, the sputtered metal is deposited on atapered wall of the etching hole 21 a, thereby closing the etching hole21 a. In the polysilicon film 14 of an electronic device according to amodification shown in FIG. 3(b), an etching hole 21 b having a steppedshape is disposed. In this modification, the sputtered metal isdeposited on a wall surface parallel to a main face of the steppedportion of the etching hole 21 b, thereby closing the etching hole.

In both of the modifications shown in FIGS. 5(a) and (b), the sputteredmetal is invaded into the cavity 22 in an initial process of thesputtering, and a deposited portion 16 b of metal is formed on thedetecting unit 12 of the sensor and the substrate 11. In this case, whenthe detecting unit 12 is a resistive element (a bolometer) of aninfrared sensor, for example, since, generally, metals do not transmitinfrared rays, the metal may possibly affect the detection sensitivity.In order to avoid such problem, it is preferred that the followingconfiguration be adopted.

As first means, in the case of the resistive element 151 shown in FIG.2, the etching hole is disposed in such a manner that the etching holeand the resistive element 151 are not overlapped on the passage of theinfrared rays, as less as possible. In the infrared sensor, the infraredrays converged by a lens or the like are incident on the detecting unit,so that it is sufficient that metals do not exist in a position blockingthe passage of the infrared rays. Especially when parallel infrared raysare incident on the detecting unit of the sensor in a directionperpendicular to the main face of the substrate, it is sufficient thatthe resistive element and the etching hole are not overlapped in termsof a plane.

FIG. 6 is a partiall cross-sectional view showing a configuration of aninterior of the cavity of the electronic device in the case where suchfirst means is employed. In FIG. 6, only an inner wall surface of thecavity 22 is shown, and diagrammatic representation of an appearance ofthe polysilicon film surrounding the cavity 22 is omitted. A circledepicted by a dashed line in the figure indicates a metal sealing member16 a for closing the etching hole. As shown in the figure, when theresistive element 31 as the bolometer of the infrared sensor and thesupporting member 32 are disposed in the cavity 22, the resistiveelement 31 and the metal sealing member 16 a for closing the etchinghole are disposed in such a manner that they do not mutually overlap inan incident direction of the infrared rays. Thus, it is possible toprevent the deterioration in detection sensitivity because of the metalsealing member 16 a through which the infrared rays is not transmitted.

As second means, a resistive element as the detecting unit of theinfrared sensor is covered with an insulating film such as a thin oxidefilm to such a degree that the infrared rays can transmit. In such acase, even if metal is deposited thereon, the temperature of theresistive element is increased as the temperature of the metal isincreased by absorbing the infrared rays, so that the detectionsensitivity is not greatly affected. Therefore, in this case, if theresistive element overlaps the metal film for closing the etching hole,the detection of the infrared rays is calculated by subtracting theamount. Thus, it is considered that unless the metal film is conductiveto the resistive element, the metal film does not affect the detectionaccuracy. In addition, it is considered that, if the metal film forclosing the etching hole does not cover about 50% of the planar area ofthe resistive element when it is viewed from the incident direction ofthe infrared rays, the detection sensitivity is not so affected.

In the case where the second means is employed, in order to hold thearea of the detecting unit of the infrared sensor smaller, and tomaintain the detection sensitivity higher, it is preferred that themetal film for closing the etching hole be disposed so as not to cover10% or more of the planar area of the resistive element when it isviewed from the incident direction of the infrared rays.

EMBODIMENT 3

With reference to FIGS. 7A to 7N, a third embodiment according to thepresent invention will be described. FIGS. 7A to 7C are sectional viewsshowing steps before a sacrificial layer is formed in a productionprocess of an electronic device in this embodiment. FIGS. 7D to 7F aresectional views showing steps before a BPSG film is planarized after thesacrificial layer is formed in the production process of the electronicdevice according to this embodiment. FIGS. 7G to 7I are sectional viewsshowing steps before a protection film and the like are patterned afterthe BPSG film is planarized in the production process of the electronicdevice according to this embodiment. FIGS. 7J to 7L are sectional viewsshowing steps before etching holes are formed after the protecting filmand the like are patterned in the production process of the electronicdevice according to the embodiment. FIGS. 7M and 7N are sectional viewsshowing steps before a sealing member for closing the etching holes areformed after the etching holes are formed in the production process ofthe electronic device according to this embodiment.

Herein a method of fabricating a bolometer-type infrared sensor isdescribed. Alternatively, this embodiment can be applied to a method offabricating a sensor of another type.

In a step shown in FIG. 7A, a peripheral circuit portion 52 is formed ona silicon substrate 51. In the peripheral circuit portion 52, a knowndevice such as MOS transistors or diodes are formed.

Next, in a step shown in FIG. 7B, a silicon oxide film 53 which coversthe silicon substrate 51 and the peripheral circuit portion 52 is formedby CVD.

In a step shown in FIG. 7 c, after a polysilicon film is deposited onthe silicon oxide film 53, the polysilicon film is patterned, therebyforming a first sacrifice polysilicon layer 55. The first sacrificepolysilicon layer 55 is removed in a later step, thereby defining theshape of a lower cavity.

In a step shown in FIG. 7D, after a silicon oxide film 56 which coversthe entire of the substrate 51 is formed by CVD, an upper face of thesilicon oxide film 56 is planarized. The planarization is performed by amethod of CMP, etching back, or the like.

In a step shown in FIG. 7E, after a polysilicon film is deposited on thesilicon oxide film 56, and then patterned, thereby forming a resistiveelement 57 functioning as a bolometer. The resistive element 57 has thesame planar shape as that of a resistive element 31 shown in FIG. 11. Asthe resistive element 57; a metal of titan (Ti) or the like may be used,instead of polysilicon.

In a step shown in FIG. 7F, a BPSG (borophosphor silicate glass) film 59which covers the silicon oxide film 56 and the resistive element 57 isdeposited. Thereafter, planarization is performed by reflow. The BPSGfilm 59 is disposed so as to electrically insulate the Al wiring fromthe peripheral circuit portion 52 and the resistive element 57. For thisreason, instead of the BPSG film 59, another insulating film can beused.

Next, in a step shown in FIG. 7G, contact holes which reach the deviceof the peripheral circuit portion 52 and the resistive element 57,respectively, are formed through the BPSG film 59. Thereafter, an Alalloy film is deposited in the interior of each of the contact holes andon the BPSG film 59. Then, the Al alloy film is patterned, so as to formAl wiring 60 for connecting the resistive element 57 to the device ofthe peripheral circuit portion 52.

In a step shown in FIG. 7H, a protecting film 62 of silicon nitridewhich covers the Al wiring 60 and the BPSG film 59 is formed.

In a step shown in FIG. 7I, a groove 63 is formed through the protectingfilm 62, the BPSG film 59, and the silicon oxide film 56, and the groove63 reaches the first sacrifice polysilicon layer 55. The planar layoutof the groove 63 at this time is shown in FIG. 8. The groove 63 isformed so as not to run across the Al wiring 60.

In a step shown in FIG. 7J, a polysilicon film is deposited in the hole63 and on the protecting film 62. Thereafter the polysilicon film ispatterned, thereby forming a second sacrifice polysilicon layer 65having a thickness of about 1 μm. The second sacrifice polysilicon layer65 is removed later together with the first sacrifice polysilicon layer55, thereby defining the shape of an upper cavity.

In a step shown in FIG. 7K, a silicon oxide film 64 having a thicknessof about 2 μm is deposited by CVD so as to cover the second sacrificepolysilicon layer 65 and the protecting film 62. Thereafter, the upperface of the silicon oxide film 64 is planarized by CMP or othertechniques.

In a step shown in FIG. 7L, a number of etching holes 66 are formedthrough the silicon oxide film 64, and the etching holes 66 reach thesecond sacrifice polysilicon layer 65. The diameter of an etching hole66 is 0.3 μm or more, for example.

In a step shown in FIG. 7M, a CF₄ gas is introduced to the secondsacrifice polysilicon layer 65 and the first sacrifice polysilicon layer55 through the etching holes 66, so as to remove the first and secondsacrifice polysilicon layers 55 and 56. As the result of this treatment,an upper cavity 68 is formed above the resistive element 57 as aninfrared detecting unit of the infrared sensor and the supporting member67 for supporting this, and a lower cavity 69 is formed below them.Specifically, the resistive element 57 and the substrate 51 areconnected only by a supporting column 67 a of the supporting member 67,so that the resistive element 57 is almost insulated from the siliconsubstrate 51.

In a step shown in FIG. 7N, an Al film 70 is deposited in the interiorof the etching holes 66 and on an upper face of the silicon oxide film24 by sputtering in an oblique direction with respect to the substrate51. At this time, the sputtering is performed under a pressure of 10 Paor less. If the pressure exceeds 10 Pa, the heat insulating property inthe cavity is insufficient. In the case where the diameter of theetching hole 66 is 0.3 μm, for example, the thickness of the Al film 70can be set to be 2.0 μm, for example. In order to close the etching hole66 having a diameter of 0.3 μm, it is necessary that the Al film 70 hasa thickness of 1.7 μm or more. In addition, if the diameter of theetching hole 66 is increased, the thickness of the Al film 70 depositedby sputtering is required to be increased accordingly.

According to this embodiment, in the step shown in FIG. 7N, the Al film(the metal sealing member) for closing the etching holes 66 is depositedby sputtering. For this reason, as compared with the case of CVD, theetching holes 66 can be closed under a much lower pressure (a highervacuum level). Therefore, the vacuum levels of the upper cavity 68 andthe lower cavity 69 can be held to be high. Especially when the etchingholes are closed by sputtering under a pressure of 5 Pa or less, thepressure of the upper cavity 68 and the lower cavity 69 can be held tobe a pressure of 5 Pa or less. As a result, the thermal conductivityfrom the detecting unit of the sensor disposed between the upper cavity68 and the lower cavity 69 via surrounding space can be reduced. Thedetection sensitivity of the sensor can be improved to be about threetimes or more as much as the prior art. In addition, it is unnecessaryto perform the thermal treatment after the polysilicon film for closingthe etching holes is deposited as in the conventional productionprocess. Therefore, the aluminum wiring and the like are not badlyaffected, and the sensitivity of the sensor can be improved.

As shown in FIG. 70, etching back is performed, and the etching holes 66are closed by a metal sealing member 70 a.

In this embodiment, a metal is used for closing the etching holes 66.Thus, there exists almost no polysilicon film which adsorbs a gas or thelike in the upper cavity 68 and the lower cavity 69, as in the case ofCVD. Therefore, there arises no problem that a residual gas or the likeis discharged into the respective cavities 68 and 69 during the use ofthe electronic device, so that the vacuum level is deteriorated.

In the production process of the infrared sensor of this embodiment, thewall portion for sealing the bolometer (the resistive element 57) of theinfrared sensor and the supporting member 67 is constituted by siliconoxide or silicon nitride, and the sacrificial layers are formed frompolysilicon, so that the following advantages are attained. When thesacrifice polysilicon layers 55 and 65 are to be etched, a CF₄ gas isused. As compared with the polysilicon layer, an etching rate for theoxide film or the nitride film by the CF₄ gas is smaller. Therefore, theoxide film and the nitride film (the material constituting thesupporting member 67) which support the resistive element 57 as thedetecting unit of the infrared sensor are not removed by the CF₄ gas.Thus, it is unnecessary to dispose an etch stop layer around the oxidefilm or the nitride film. Therefore, the process flow in the case wherethe detecting unit of the infrared sensor is disposed in the cavity issimplified.

In this embodiment, an example in which the CF₄ gas is used for etchingthe sacrifice polysilicon layers 55 and 56 is described. Instead of theCF₄ gas, an etchant such as KOH or TMAH, or an etching gas such as XeFmay be used. Especially when an etchant is used, it is possible tomaintain a high etching selective ratio of the sacrifice polysiliconlayers 55 and 56 to the silicon oxide film.

In the step shown in FIG. 7N, it is desired that the sputtering beperformed with holding the temperature in the chamber at 400° C. to 500°C. while the Ar gas is introduced into the chamber at a flow rate of 10to 30 (ml/min). In the case where the temperature in the chamber duringthe sputtering is less than 400° C., the velocity of reflow of thesputtered Al particles is reduced, and a portion in which the growthspeed of Al film is low is generated. Therefore, it takes an extremelylong time to close the etching holes. On the other hand, when thetemperature in sputtering exceeds 500° C., the temperature badly affectsthe Al wiring 60 and the like.

In the case where the sputtering in the oblique direction is notperformed, the distance between the sputtering target and the substrateis desirably 10 cm or less. In long throw sputtering in which thedistance between the sputtering target and the substrate is 10 cm ormore, the ratio of metal particles vertically incident on the upper faceof the substrate is increased, so that the velocity at which the metalfilm is deposited on the side wall surface of the etching hole islowered. Thus, it takes much more time to close the etching hole, andthe number of metal particles invaded into the cavity is increased.

For example, in the case where the Ar gas is introduced into the chamberat a flow rate of 10 to 30 (ml/min), the temperature in the chamber isheld at 400° C. to 500° C., and the distance between the sputteringtarget and the substrate is 10 cm or less, a metal film of about 600 nmis deposited on the upper face of the substrate for about 40 seconds,unless the sputtering in the oblique direction is performed. At the sametime, the etching holes each having a diameter of 0.3 μm is closed.

In the step shown in FIG. 7N, metals to be sputtered includes, inaddition to the aluminum (Al), other metals such as tungsten (W),titanium (Ti), molybdenum (Mo), copper (Cu), tantalum (Ta), barium (Ba),strontium (Sr), platinum (Pt), and rubidium (Rb), and compounds thereof.Any of the metals may be employed.

In a current semiconductor process of 0.13 μm rule, for the sputteringof Cu or Ta, generally, the metal to be sputtered is ionized bygenerating plasma at a pressure of several Pa, so as to increase thedirectivity. On the other hand, Al, Ti, or W is sputtered at a lowpressure of about 100 mPa. Therefore, in the case where the pressure inthe cavity is desired to be held at a low pressure of about 100 mPa, itis preferred that the sputtering of Al, Ti, or W be performed. In thecase of a sensor which does not require not so high vacuum such as aninfrared sensor, the sputtering may be performed at a pressure of 5 Paor less. If the sputtering is performed at a pressure of 10 Pa or less,the detection sensitivity of the sensor can be sufficiently improved ascompared with the conventional production method.

Also in this embodiment, an optimal range of inclination in the obliquesputtering can be defined similarly to the first embodiment. The shapeof the etching hole can be considered similarly to the first embodimentand the modification thereof.

EMBODIMENT 4

Hereinafter a fourth embodiment of the present invention will bedescribed.

In general, step coverage of a thin film deposited by sputtering is notso high. Therefore, in the case where the oblique sputtering is notused, the deposition rate of a metal film on a sidewall of an etchinghole is smaller than the deposition rate on an upper face of asubstrate. That is, in order to close the etching holes by a metalsealing member, the aspect ratio is preferably larger than 1. However,as the thickness of a silicon oxide film 64 is increased, the amount ofabsorption of infrared rays by the silicon oxide film 64 is increased.Thus, the sensitivity of the infrared sensor is deteriorated.

Therefore, in order to maintain the sensitivity of the infrared sensorhigh and to easily close the etching holes by the metal sealing member,it is considered that the size of each etching hole is reduced. However,if the size of each etching hole is reduced, the efficiency in etching asacrifice polysilicon layer may be disadvantageously degraded. In thismodification, a method for improving the efficiency in etching thesacrifice polysilicon layer is described.

FIG. 9 is a view showing a configuration in a step corresponding to thestep shown in FIG. 7L of the infrared sensor according to thisembodiment. The final configuration of the infrared sensor of thisembodiment is almost the same as that of the infrared sensor in thethird embodiment shown in FIG. 70, but is different in the followingpoint.

In this embodiment, in the step shown in FIG. 7L in the thirdembodiment, when etching holes 66 are formed in a silicon oxide film 64,side etching holes 66 a which are in contact with side portions of thesecond sacrifice polysilicon layer 65 are formed. With the provision ofthe side etching holes 66 a, an etchant is introduced to the secondsacrifice polysilicon layer 65 from the side faces thereof. Thus, theetching efficiency of the second sacrifice polysilicon layer 65 isincreased. Therefore, if a diameter of each etching hole 66 is reduced,the etching efficiency of the second sacrifice polysilicon layer 65 andthe first sacrifice polysilicon layer 55 is not lowered. Therefore, inthe case where the thickness of the silicon oxide film 64 is notchanged, the etching holes 66 can be rapidly closed by the metal sealingmember. Alternatively, the thickness of a portion of the silicon oxidefilm 64 positioned above the second sacrifice polysilicon layer 65 isreduced, so that the sensitivity of the infrared sensor can beincreased.

On the other hand, the side etching holes 66 a reach the surface portionof the protecting film 62 through the silicon oxide film 64. Since theside etching holes 66 a are not through holes, it is possible torelatively easily close the side etching holes 66 a by the metaldeposited on both of the bottom face and the side face of the sideetching holes 66 a in a later step of closing the etching holes 66 bysputtering a metal (the step shown in FIG. 7N). In addition, even if themetal film is deposited on the side face of the upper cavity 65, themetal film does not badly affect the sensitivity and the performance ofthe sensor such as an infrared sensor. Thus, a diameter of the sideetching hole 66 a may be larger than that of the other etching holes 66.Instead of the side etching holes 66 a, an etching groove may be formedalong the side face of the second sacrifice polysilicon layer 65. Theside etching holes 66 a (or the etching groove) are not required toreach the protecting film 62, but may be formed by digging only an upperportion of the silicon oxide film 64.

EMBODIMENT 5

Hereinafter a fifth embodiment according to the present invention willbe described.

This embodiment describes a method in which a step of closing theetching holes after the etching of the sacrifice polysilicon layers isperformed by a combination of CVD and sputtering.

FIGS. 10A to 10C are sectional view showing production stepscorresponding to FIGS. 7M to 7N of an infrared sensor according to thisembodiment.

In this embodiment, in the step shown in FIG. 10A, a CF₄ gas isintroduced to the second sacrifice polysilicon layer 65 and the firstsacrifice polysilicon layer 55 through the etching holes 66, therebyremoving the first and second sacrifice polysilicon layers 55 and 65. Asthe result of this treatment, an upper cavity 68 is formed above aresistive element 57 as an infrared detecting unit of the infraredsensor and a supporting member 67 for supporting this, and a lowercavity 69 is formed below them. Specifically, the resistive element 57and the supporting member 67 are conducted only by a supporting column67 a of the supporting member 67. Thus, the resistive element 57 isalmost thermally insulated from a silicon substrate 51.

Next, in the step shown in FIG. 10B, a polysilicon film 71 having athickness of about 50 nm, for example, is deposited by CVD on an exposedsurface. As the result of this treatment, an opening area of the etchinghole 66 is reduced.

Next, in the step shown in FIG. 10C, an Al film 70 is deposited bysputtering in the etching holes 66 and on the upper face of thesubstrate. At this time, the sputtering is performed under a lowpressure in the range of 10 Pa or less. By the deposition, the etchingholes 66 are closed by the Al film 70.

Diagrammatic representation of succeeding steps is omitted, butsimilarly to the step shown in FIG. 70, etching back of the Al film 70is performed, thereby removing a portion of the Al film 70 positionedabove the upper face of the substrate. The metal sealing member is leftonly in the etching holes 66.

According to this embodiment, in the step shown in FIG. 10A, the firstand second sacrifice polysilicon layers 55 and 65 can be rapidly andsurely removed by using relatively larger etching holes 66 (a diameterof 0.35 μm, for example). In the step shown in FIG. 10C, etching holes66 of which the diameter is reduced (for example, 0.3 μm) can be closedby Al in a shorter period of time. After the step shown in FIG. 10C, aneffect that the time required for etching back of the Al film 70 isshortened is attained.

Even if the polysilicon film 71 is deposited on the wall surfaces of therespective cavities 68 and 69 and on the surface of the supportingmember 67, the polysilicon film 71 transmits infrared rays, so that thedeposition does not affect the sensitivity of the infrared sensor.Alternatively, in the case where a silicon oxide film is depositedinstead of the polysilicon film 71, when the thickness is sufficientlythin (about 50 nm, for example), the deposition does not affect thesensitivity of the infrared sensor.

EMBODIMENT 6

Hereinafter a sixth embodiment according to the present invention willbe described.

FIG. 11 is a view showing a configuration in a step corresponding to thestep shown in FIG. 7L of an infrared sensor according to thisembodiment. The final configuration of the infrared sensor in thisembodiment is almost the same as that of the infrared sensor shown inFIG. 7O, but is different in the following points.

In this embodiment, in the step shown in FIG. 7L, after the siliconoxide film 64 is deposited, the silicon oxide film 64 is planarized byCMP or the like until the upper face of the silicon oxide film 64 is atthe same level of the upper face of the second sacrifice polysiliconlayer 65. Thereafter, on the entire surface of the substrate, a siliconoxide film 73 having a thickness of about 5 nm and a polysilicon film 74having a thickness of about 500 nm are sequentially deposited by CVD.Thereafter, a relatively large opening having a diameter of about 0.4 μmis formed in the polysilicon film 74. Then, after a silicon oxide film75 having a thickness of about 50 nm is deposited on the entire surfaceof the substrate by CVD, portions of the silicon oxide films 75 and 73corresponding to the positions of the openings of the polysilicon film74 are removed, thereby forming etching holes 66 which reach the secondsacrifice polysilicon layer 65. For example, by the above-describedprocess, the configuration shown in FIG. 11 is formed. By a processwhich is different from the process as described above, theconfiguration shown in FIG. 11 can be obtained.

According to this embodiment, the whole of the contour portionsurrounding the etching holes 66 when the first and second sacrificefilms 55 and 65 are etched is not configured by a silicon oxide film,but the polysilicon film 74 is covered with the silicon oxide films 73and 75. In this case, the thickness of the silicon oxide film whichabsorbs the infrared rays is greatly reduced (100 nm in total in thisexample) as compared with the second embodiment. Thus, it is possible tosuppress the deterioration of the sensitivity of the infrared sensor. Onthe other hand, the periphery of the polysilicon film 74 is covered withthe silicon oxide films 73 and 75, so that there is no trouble foretching the first and second sacrifice polysilicon layers 55 and 65.

In the first and second embodiments, and in the respectivemodifications, examples in which the invention is applied to theinfrared sensor are described. The electronic devices to which thepresent invention is applied include, other than the infrared sensor, apressure sensor, an acceleration sensor, a flow-rate sensor, a vacuumtransistor, and the like. The infrared sensor is generally classifiedinto a thermal type such as a bolometer, a pyroelectric-type sensor, anda thermopile, and a quantum type using PbS, InSb, HgCdTe, and the like.Some bolometers utilize the resistance law of polysilicon, Ti, TiON,VO_(x) or the like. In addition, some utilize a transient property of aforward current of a PN diode or the like. Some thermopiles utilize aSeebeck effect caused in a PN junction. Some pyroelectric-type infraredsensors utilize a pyroelectric effect of a material such as PZT, BST,ZnO, PbTiO₃. Some utilize the variation in dielectric constant of thesematerials. The quantum-type infrared sensor detects a current caused byelectronic excitation. For example, there is an infrared sensor having achromel-alumel thermocouple for detecting infrared rays by Seebeckeffect, or the like.

As for the above-mentioned infrared sensors, in order to maintain thedetection sensitivity for infrared rays, and the accuracy in detectionof the infrared rays high, it is preferred that heat dissipation fromthe infrared detecting unit be small. The characteristics of such aninfrared sensor are improved, when it is sealed in a cap unit in avacuum atmosphere or in an inert gas atmosphere.

As for the pressure sensor and the acceleration sensor, it is known thatthe sensitivity thereof is increased by reducing the viscous resistanceof the air, so that the characteristics are improved when it is sealedin a cap unit in a vacuum atmosphere or an inert gas atmosphere.

In the above-described respective embodiments, a metal sealing member ofAl is used as the sealing member for the present invention.Alternatively, it is possible to use metals other than Al, or conductivematerials which can be sputtered such as polysilicon as the sealingmember of the present invention.

EMBODIMENT 7

Hereinafter with reference to the drawings, a seventh embodimentaccording to the present invention will be described.

An electronic device of this embodiment is an image sensor in which bothof infrared detecting units and visible-light detecting units areintegrated on one and the same substrate. An exemplary configuration ofan image sensor provided with infrared detecting units and visible-lightdetecting units is disclosed in Japanese Laid-Open Patent PublicationNo. 2003-17672, for example.

By arranging both of the infrared detecting units and the visible-lightdetecting units on one and the same substrate by using a semiconductorprocess, the production cost can be reduced, and the device can beminiaturized. In the case where an image sensor for infrared rays and animage sensor for visible light are disposed on separate substrates, itis necessary to perform optical alignment accurately, and to correct adeviation between the infrared image and the visible-light image.According to this embodiment in which both are integrated on one and thesame substrate (one chip), such problems can be solved.

The electronic device of this embodiment includes, as shown in FIGS.12(a) and (b), a silicon substrate 160, a plurality of infrareddetecting units 161 and visible-light detecting units 162 arranged in amatrix (in an array) of rows and columns on the silicon substrate 160,and a reading circuit. The reading circuit is constituted by a verticalscanning register 164 and a horizontal scanning register 165.

The plurality of infrared detecting units 161 arranged on the siliconsubstrate 160 are covered with individual micro vacuum packages 163,respectively. For easy understanding, in FIG. 12(a), the micro vacuumpackage 163 is shown as a package member which is different from theabove-described cavity formed by using a semiconductor process such asthin-film deposition, photolithography, and patterning technique, butalso in this embodiment, the cavity is formed by using the semiconductorprocess similarly to the above-described embodiments.

FIGS. 12(a) and (b) schematically show the arranged relationships of therespective units, but does not represent precisely the specific shape orscale of the configuration of the actual electronic device. The actualinfrared detecting unit 161 is preferably designed to be larger (to havea size of about 50 μm, for example) than the visible-light detectingunit 162 so that a predetermined sensitivity is attained. In the casewhere the size of the infrared detecting unit 161 is remarkably largerthan the size of the visible-light detecting unit 162, a preferredlayout for arrangement of the infrared detecting units 161 and thevisible-light detecting units 162 is not the same as the layout shown inFIG. 1.

FIG. 13 is a perspective view schematically showing a configuration of arepresentative example of the infrared detecting unit 161 shown in FIGS.12(a) and (b). The infrared detecting unit 161 includes an infraredabsorbing portion 166, a micro heater 167, and a micro heater supportingportion 168, and these are formed inside a cavity 163′.

The micro heater 168 is a resistive element formed from aresistivity-changeable material, and the micro heater 168 has twofunctions in this embodiment. The first function is a function ofdetecting a temperature based on resistance variation. The secondfunction is a function of generating heat by Joule heat. As describedlater, by means of the temperature detecting function of the microheater 167, the incident amount of the infrared rays is detected, and bymeans of a combination of the heat generating function and thetemperature detecting function of the micro heater 167, the vacuum level(the pressure) in the cavity can be detected.

The micro heater 167 can be formed from a semiconductor such as silicon,a metal oxide such as TiO (titania) or VO_(x) (vanadium oxide), or ametal such as Ti (titanium) or PT (platinum), or a metal silicidethereof. These materials are known as material having large coefficientof resistance law, and can attain a superior temperature detectingfunction. An impurity such as B, As, Sr, or Cu may be doped into thematerial. For example, as for polysilicon doped with B or TiO doped withSr, an electric resistance value can be controlled to be an appropriatevalue by adjusting the impurity doping level.

A planar size of the micro heater 167 in the preferred embodiment is asize falling in a rectangular area of 1 mm×1 mm. A preferred example ofthe planar layout of the micro heater 167 includes a meandering patternincluded in a rectangular area of 50 μm×50 μm, as shown in FIG. 14, sothat a relatively long pattern of resistive element is formed in arelatively small area to be occupied.

The micro heater 162 in this embodiment is held, as shown in FIG. 13, bythe micro heater supporting portion 168 in a position (a position higherby 1 μm, for example) distant from the surface of the silicon substrate160 (FIG. 12(a)).

If the position of the rectangular region for defining the planar sizeof the micro heater 167 exceeds 1 mm, the distortion caused in the microheater 167 is increased. Therefore, it is necessary to further increasethe distance between the micro heater 167 and the substrate 160. If themicro heater 167 is designed to be larger, the electronic device cannotbe miniaturized. Therefore, it is preferred that the micro heater 167 bedesigned to have a size falling in a rectangular region of 1 mm×1 mm.Such a small micro heater 167 is obtained by, after a thin film of amaterial exhibiting the above-described functions is deposited by thinfilm deposition technique, patterning the thin film so as to have adesired shape by photolithography and etching techniques. The thicknessof the thin film is set in the range of 50 nm to 1 μm, for example.

The infrared absorbing portion 166 is formed from a material which canabsorb infrared rays, for example, SiO₂. When the infrared detectingunit 166 formed from such a material receives the irradiation ofinfrared rays, it generates heat by absorbing the infrared rays. As aresult, the temperature of the infrared absorbing portion 166 isincreased, and accordingly the temperature of the micro heater 167 isincreased. Since the micro heater 167 is formed from aresistivity-changeable material, the electric resistance is varied asthe rise of temperature. The variation in electric resistance is readand sensed by a readout circuit (a vertical scanning register 164 and ahorizontal scanning register 165) shown in FIGS. 12(a) and (b), therebyknowing irradiation amount of infrared rays.

The micro heater supporting portion 168 separates the micro heater 167from the surface of the substrate by means of an insulator patterned asa small column having a relatively small sectional area as compared withthe length thereof, as shown in FIG. 13. The thermal conductivity of themicro heater supporting portion 168 is low, and a thermal conductancebetween the micro heater 167 and the substrate 160 is low. Therefore, itis possible to increase the amount of rise in temperature of the microheater 167 when the infrared rays are incident, so that the detectionsensitivity for infrared rays is improved.

The thermal conductance between the micro heater supporting portion 168and the substrate 160 can be previously obtained by calculation, whenthe shape and the material of the micro heater supporting portion 168are determined. For example, as shown in FIG. 15, the micro heatersupporting portion 168 has a square plate shape having a side of about50 μm supported by two columns each having a sectional area of 3×3 μm²and a length of about 50 μm, and is formed from Si₃N₄, the thermalconductance is calculated to be 3×10⁻⁷ W/K. The small micro heatersupporting portion as shown in FIG. 15 can be produced by using thetechnique of MEMS (Micro Electro Mechanical Systems).

The visible-light detecting unit 162 shown in FIGS. 12(a) and (b) isconstituted by a photodiode, for example, and can detect the amount ofincident visible light by measuring a current or a voltage generated inaccordance with the amount of incident visible light. The visible-lightdetecting unit 162 in this embodiment is preferably formed by doping aselected region of the surface of the silicon substrate 160 with animpurity. The visible-light detecting unit 162 can be formed by a stepof forming a readout circuit on the silicon substrate, or a step beforeor after the step of forming the readout circuit. The visible-lightdetecting unit 162 is formed before a manufacturing step of the infrareddetecting unit 161 in a preferred embodiment.

In this embodiment, the infrared detecting unit 161 and thevisible-light detecting unit 162 are formed on one and the same siliconsubstrate by the semiconductor process, so that it is possible toprovide an image sensor which is formed in one chip for infrared raysand visible light at a low cost.

The intensities of infrared rays and visible light incident on theinfrared detecting unit 161 and the visible-light detecting unit 162,respectively, are converted into electric signals in the correspondingdetecting units. The electric signals are sequentially read out byreadout circuits (164, 165). The infrared detecting units 161 and thevisible-light detecting units 162 are arranged in a matrix on one andthe same substrate, so that electric signals corresponding to aninfrared image and a visible light image can be obtained. An imagingmethod by light detecting units arranged in a matrix is disclosed indetail in Japanese Laid-Open Patent Publication No. 11-326037, forexample.

The micro vacuum package portion in this-embodiment covers individualinfrared detecting units 161 and the interior thereof is maintained in acondition of a reduced pressure (about 50 mTorr, for example). Bylowering the pressure of the atmospheric gas of the infrared detectingunits 161, the thermal conductance between the micro heater 167 and thesubstrate 160, and the thermal conductance between the micro heater 167and the exterior atmosphere can be reduced and the detection sensitivityfor infrared rays can be improved.

Each vacuum package can take various forms. For example, as shown inFIG. 15, the package includes an internal space having a size capable ofincluding the micro heater supporting portion 168. The height of theinternal space can be set to be about 3 to 1000 μm, for example.

The micro vacuum package portion can be generally fabricated by a methoddisclosed in Japanese Laid-Open Patent Publication No. 11-326037.Specifically, the micro vacuum package portion can be fabricated byforming annular joining faces of metal, for example, on opposed faces ofa cap unit and a substrate which are previously prepared, and then byjoining the joining faces by pressure in a high vacuum. However, when acavity is formed by the semiconductor process (thin-film deposition,photolithography, etching, and the like), the production cost can bereduced, and the device can be miniaturized.

(Method of Detecting the Vacuum Level)

Next, an exemplary method of detecting an internal pressure (the vacuumlevel) of the micro vacuum package in this embodiment will be described.

Since the micro heater 167 in this embodiment is formed from aresistivity-changeable material as described above, the electricresistance of the micro heater 167 is varied depending on thetemperature. Therefore, if the electric resistance of the micro heater167 is measured by causing a current to flow from the external to themicro heater 167, the temperature of the micro heater 167 can beobtained.

On the other hand, an electric resistance (a value at a predeterminedtemperature) and a current of the micro heater 167 are measured in acondition where it is not irradiated with infrared rays. By using themeasured values of the electric resistance and the current, an amount ofheat generation Q per unit time from the micro heater can be calculatedfrom Joule's law. That is, when the measured electric resistance of themicro heater 167 is represented by R (ohm), and a current flowingthrough the micro heater 167 is represented by I (ampere), Q can becalculated by using the following expression:Q=I²R (watt).

Therefore, when the current I and the electric resistance R flowingthrough the micro heater 167 are measured, the amount of heat generationQ from the micro heater 167 can be known. At this time, the temperatureof the micro heater 167 in a condition where a current is caused to flowto the micro heater 167 is represented by T, the temperature of thesubstrate 160 is represented by TO, and the thermal conductance betweenthe micro heater 167 and the exterior is represented by g, the followingrelationship expression is established:(T−TO)×g=Q.

The thermal conductance g between the micro heater 167 and the exterioris, as shown below, a sum of the thermal conductance g_(S) relating tothe heat flowing through the micro heater supporting portion 168 and thethermal conductance g_(A) relating to the heat flowing through theatmospheric gas in the inside the vacuum package.g=g _(S) +g _(A)

From the above two expressions, the following relationship expression isobtained.(T−TO)×(g _(S) +G _(A))=Q

When the expression is transformed, the following expression isobtained.g _(A) =Q/(T−TO)−g_(S)

Among the parameters of the right side of this expression, Q iscalculated from the current I and the electric resistance R flowingthrough the micro heater 167. The parameter g_(S) is a constant which ispreviously measured, and the substrate temperature TO can be dealt as aconstant of about a room temperature. Therefore, by measuring thetemperature T, g_(A) can be obtained by calculation.

On the other hand, the relationship between the thermal conductanceg_(A) via the atmospheric gas and the pressure of the atmospheric gascan be obtained by simulation or experiments. Therefore, if the thermalconductance g_(A) via the atmospheric gas is obtained, the pressureinside the micro vacuum package can be known.

In order to obtain the relationship between the thermal conductanceg_(A) via the atmospheric gas and the pressure of the atmospheric gas byexperiments, a test device including a macro vacuum package with a smallopening may be prepared, as shown in FIG. 16, and the test device may bedisposed in a vacuum chamber, for example. Via the opening of the microvacuum package, the difference in pressure between the inside and theoutside of the micro vacuum package is eliminated. Thus, g_(A) may beobtained from the above expression with changing the internal pressureof the vacuum chamber, so as to determine the dependency on pressure ofg_(A).

Next, with reference to FIGS. 17A to 17D, an exemplary specificconfiguration of the micro heater 167 preferably employed in thisembodiment will be described.

FIG. 17A is a perspective view showing the micro heater 167 formed in arectangular cavity (the micro vacuum package). FIG. 17B is a sectionalview taken along a plane parallel to the XZ plane. FIG. 17C is asectional view taken along a plane parallel to the YZ plane. FIG. 17D isa view showing a layout in a plane parallel to the XY plane.

As shown in FIGS. 17B to 17D, a bridge (a member functioning as both ofthe micro heater and the micro heater supporting portion) formed in arectangular parallelepiped cavity having a width of about 20 μm, aheight of about 3 μm, and a length of a longer side of about 100 μm isprovided. The thickness of the bridge is about 1 μm, and the widththereof is about 8 μm, and the bridge extends in the substantiallycenter portion of the cavity 163′ in the longer side direction (thelength of about 100 μm).

The bridge in this embodiment is formed from silicon doped with animpurity (dopant such-as boron). Selected regions (two parallel linearregions) of the bridge are doped with the impurity at a higher densitythan the other regions, so as to lower the resistance. One end of thehigher density impurity region of lower resistance which linearlyextends is electrically connected to one of a pair of aluminum electrodepads, so as to exhibit the same function as that of a conductive wiring.A predetermined voltage is applied across the pair of aluminum electrodepads, a current flows in a portion in which the impurity density isrelatively low in the bridge along a shorter side direction of thebridge.

FIG. 18 is a graph showing an example of the relationship between theelectric resistance and the vacuum level (the pressure) in the microheater shown in FIGS. 17A to 17D. As is seen from the graph, the currentflowing through the micro heater is reduced in accordance with theincrease in pressure. This means that the temperature rise in the microheater is reduced in accordance with the increase in pressure, and as aresult, the reduction in electric resistance in the micro heater becomessmall.

FIGS. 17A to 17D show an example of the length and the width of theresistive element in the micro heater 167, and the configuration of theactual micro heater is not limited to those shown in the figures.

The micro heater 167 in this embodiment is not only used for measuringthe vacuum level, but also used for measuring the irradiation amount ofinfrared rays. In the case where infrared rays are detected in the microheater in the above-described manner, it is desired that a foldingpattern be applied to the micro heater for the purpose of increasing thelight receiving area.

When the relationship between the current (the electric resistance) andthe vacuum level as shown in FIG. 18 is used, the vacuum level (thepressure) inside the micro vacuum package (inside the cavity) can beobtained in real time, by measuring the current (the electricresistance) of the micro heater.

Next, with reference to FIGS. 19 to 33, a method of fabricating themicro heater and the micro vacuum package will be described. Figures (c)in FIGS. 19 to 33 are plan views showing main portions of the substrate.Figures (a) are sectional views taken along a line A-A′ in (c). Figures(b) are sectional views taken along a ling B-B′ in (c).

First, as shown in FIG. 19, a readout circuit (a transistor or the like)is formed on a silicon substrate 160. The readout circuit is preferablyconstituted by a CMOS circuit integrated on the silicon substrate, andmanufactured by a known semiconductor integrated circuit manufacturingtechnique. Thereafter, although not shown in the figure, visible-lightdetecting units are formed on the silicon substrate 160.

Next, as shown in FIG. 20, by a thin film deposition technique such asCVD, a silicon oxide film (the thickness of about 100 nm) 170 isdeposited so as to cover the entire upper face of the silicon substrate160.

Thereafter, as shown in FIG. 21, a polysilicon layer 171 having athickness of about 1 μm is formed in a region in which infrareddetecting units are to be formed. The polysilicon layer 171 can befabricated by depositing a polysilicon film on the silicon oxide film170 by CVD, for example, and thereafter by patterning the polysiliconfilm by photolithography and etching techniques. The polysilicon layer171 functions as a “first sacrificial layer” which is finally removed byetching. In the example shown in FIG. 21, the polysilicon layer 171 hasa rectangular planar shape, and the micro heater is formed above thepolysilicon layer 171.

Next, as shown in FIG. 22, after a second silicon oxide film 172 isdeposited so as to cover the polysilicon layer 171, an upper face of thesecond silicon oxide film 172 is planarized. The planarization isperformed so as to leave the silicon oxide film 171 having a thicknessof about 250 nm on the polysilicon layer (the first sacrificial layer)171. The silicon oxide film 172 on the polysilicon layer (the firstsacrificial layer) 171 functions as an etch stop layer for a lowerportion of the micro heater in a step of etching the polysilicon layer(the first sacrificial layer).

Next, as shown in FIG. 23, a micro heater 173 of polysilicon doped withB (boron) is formed in a region in which infrared detecting units are tobe formed. The micro heater 173 is fabricated by depositing a secondpolysilicon film on the second silicon oxide film 172, for example, andinjecting B ions into the second polysilicon film, and then bypatterning the second polysilicon film by photolithography and etchingtechniques. Instead of the separate steps of deposition of the secondpolysilicon film and the injection of B ions, a dopant gas may be addedto silane gas or the like which is a material for polysilicon during thedeposition of the second polysilicon film. The impurity with which thesecond polysilicon film is doped is not limited to B.

Thereafter, by injecting ions such as BF₂ into selected regions of thesecond polysilicon film, the doping level of the injected regions isrelatively increased, and the electric resistivity (the specificresistance) is reduced. In this way, a region functioning as a resistiveelement and a region functioning as a wiring portion as shown in FIG.17D can be formed in polysilicon.

Next, as shown in FIG. 24, a third silicon oxide film 174 having athickness exceeding 1 μm is deposited, and then the film is planarized.The planarization is performed so as to leave the third silicon oxidefilm 174 having a thickness of about 1 μm on the micro heater 173. Thethird silicon oxide film 174 has a function as an interlayer insulatingfilm positioned between the upper and lower wirings, a function as anetch stop layer for the upper portion of the micro heater in the etchingprocess of the sacrificial layer, and a function as an infraredabsorbing portion.

Next, as shown in FIG. 25, in order to electrically connect the microheater 173 and the readout circuit, a contact hole 175 is formed in thesilicon oxide film, and a wiring portion 176 is formed. The contact hole175 is formed in such a manner that a predetermined portion of thesilicon oxide film is removed by photolithography and etchingtechniques. The wiring portion 176 is formed by depositing a film of awiring material such as aluminum on the third silicon oxide film 174 andthen by patterning the film by photolithography and etching techniques.The wiring portion 176 is patterned so as to connect the micro heater173 and the readout circuit via the contact hole 175.

Next, as shown in FIG. 26, openings (etching holes) 177 are formed inthe third silicon oxide film (the etch stop layer for the upper portionof the micro heater) 174 and the second silicon oxide film (the etchstop layer for the lower portion of the micro heater) 172, so as toexpose a portion of the polysilicon layer (the first sacrificial layer)171. The openings function as a space for thermal insulation between theinfrared detecting units and the side face of the vacuum package.

Next, as shown in FIG. 27, after a fourth silicon oxide film having apredetermined thickness is deposited, a polysilicon layer (thickness ofabout 1 μm) 178 functioning as a second sacrificial layer is formedthereon. The polysilicon layer is also formed by patterning thedeposited polysilicon film by photolithography and etching techniques.

Next, as shown in FIG. 28, a fifth silicon oxide film 179 is deposited,and then planarization is performed. The planarization is performed sothat the fifth silicon oxide film 179 positioned on the polysilicon filmfunctioning as the second sacrificial layer has a thickness of about 500nm. The fifth silicon oxide film 179 eventually functions as a wallsurface of the vacuum package.

Next, as shown in FIG. 29, an etching hole 180 having a diameter ofabout 0.3 μm is formed in the fifth silicon oxide film 179. Thereafter,as shown in FIG. 30, an XeF₂ gas is introduced through the etching hole180, thereby etching the polysilicon layer functioning as a sacrificiallayer. As the result of the etching, a cavity 163′ is formed in a regionsurrounding the micro heater.

Next, as shown in FIG. 31, a silicon film 181 having a thickness ofabout 2 μm is deposited on the fifth silicon oxide film by sputtering.The deposition of the silicon film 181 closes the etching hole 180, andseals the cavity 163′. By the sealing, the internal pressure of thecavity 163′ is held at an atmospheric gas pressure in the sputteringstep (the internal pressure of the sputter chamber). Next, part of thesilicon film (the sputtered sealing film) 181 is removed, and thenelectrode pads which are not shown are formed.

By a series of the above-described steps, the micro heater can bedisposed inside the small vacuum package (inside a cavity of a reducedpressure). In the figures which are referred to, a single micro meter isdepicted for simplicity. In a preferred embodiment, by theabove-described MEMS technique, a number of micro heaters aresimultaneously formed on one and the same substrate. Each of the microheaters is formed by a patterned thin film, so that they can befabricated by MEMS technique at a low cost.

According to this embodiment, the micro heater 173 can not only measurethe irradiation amount of infrared rays, but also detect the internalpressure of the cavity 163′. Therefore, even if an abnormal occurs inthe internal pressure of the cavity 163′ because of a defect of aproduction process, the abnormal pressure can be sensed before shippingthe product. Even in the case where the internal pressure of the cavity163′ is at an appropriate level immediately after the production, thepressure may increase during the use and due to the time elapse. In thisembodiment, the internal pressure of the cavity 163′ can be measured asrequired, or at regular intervals. Thus, it is possible to sense theabnormality in pressure.

The specific resistance of the micro heater 173 in this embodiment ispreferably designed in a range of not lower than 1×10⁻¹ Ωcm nor morethan 1×10⁵ Ωcm. If the specific resistance of the micro heater 173 islarger than the upper limit of the range, the electric resistance of themicro heater 173 is an extremely large value of 100 kΩ or more, forexample. Thus, it is difficult to detect the temperature. In the casewhere the specific resistance is smaller than the lower limit of theabove-mentioned range, the rate of change in resistance caused in themicro heater 173 is an extremely small value of 1×10⁻³ or less. Thus, itis difficult to detect the temperature.

When the micro heater 173 is formed from a thin film of a materialhaving a specific resistance in the range of not lower than 5×10² Ω cmnor more than 5 Ω cm, the thickness of the thin film is set to be 500 nmor less. In addition, preferably, the resistance of the resistiveelement portion in the micro heater 173 is designed to be 100 kΩ orless, and the rate of change in resistance is designed to be 0.01 ormore.

When the first sacrificial layer positioned below the micro heater 173is to be etched, for the purpose of preventing the micro heater 173 frombending in the upper direction or the lower direction, it is preferredthat a film of a material having large tensile stress be disposed onand/or under the micro heater 173. Such a film of a material havinglarge tensile stress can be formed from SiN, for example.

When the sacrificial layer is to be etched, instead of XeF₂, an etchinggas such as SF₆ or CF₄ may be used, or a drug solution such as TMAH orhydrazine may be used. The material for a film which is deposited forclosing the etching hole is not limited to silicon, and other materials(a metal such as Al) may be used. When the etching hole is closed by thedeposition of such a film and the cavity is sealed, in order to increasethe vacuum level in the cavity, it is preferred that the film isdeposited under a pressure of 10 Pa or less. Especially when the microheater 17 also functions as the infrared detecting unit as in thisembodiment, in order to increase the amount of incident infrared rays,it is preferred that the member functioning as a ceiling of the cavity(a wall portion of the cavity) is formed from a material which absorbsless infrared rays. For example, if the wall portion of the cavity isformed from silicon of which the surface is covered with a silicon oxidefilm, the amount of absorbed infrared rays is small, and the siliconoxide film preferably functions as an etch stopper.

EMBODIMENT 8

Hereinafter an eighth embodiment according to the present invention willbe described.

FIG. 32 shows an embodiment in which a gettering thin film is disposedinside the micro vacuum package (inside the cavity 163′). The getteringthin film is activated by the heat generation of the micro heater 173,so as to adsorb a gas existing inside the micro vacuum package (insidethe cavity 163′), thereby reducing the pressure.

In the above-described seventh embodiment, the silicon film 181functioning as the sealing member is formed by sputtering, therebyreducing the internal pressure of the cavity 163′. The reason why theinternal pressure of the cavity 163′ can be reduced by forming thesealing member by sputtering is that, as described above, an internalpressure of a sputter chamber (which defines the internal pressure ofthe cavity 163′) is lower than an internal pressure in a chamber of aCVD apparatus. In this embodiment, the gettering thin film is disposedinside the cavity 163′, and the effect of reducing the pressure by thegettering thin film is utilized, so that the method of forming thesealing member is not limited to sputtering, and alternatively variousthin film deposition methods including CVD can be used. Specifically,after the sealing member is formed by a known thin film depositionmethod, gettering by the gettering thin film is performed, therebyreducing the internal pressure of the cavity 163′ up to a sufficientlylow value (preferably 10 Pa or less, and more preferably 5 Pa or less).The deposition of the sealing member by CVD is performed at a pressureof about 67 Pa, for example, so that the internal pressure of the cavity163′ immediately after the sealing member is deposited by CVD is about67 Pa.

In this embodiment, the gettering thin film 185 is disposed under thesilicon oxide film which functions as an etch stop layer below the microheater 173. The thickness of the gettering thin film 185 is set to be500 nm, for example. In order to maintain the vacuum level inside themicro vacuum package high by the function of the gettering thin film185, it is necessary to set the thickness of the gettering thin film 185to be a sufficient level. A preferred thickness depends on the internalvolume of the micro vacuum package.

The electric resistance of the micro heater 173 is set to be 1 MΩ orless, for example. In a preferred example, when a voltage of 10 V isapplied to the micro heater, the heat generation is 10⁻⁴ W or more. Whenthe thermal conductance between the micro heater 173 and the external isset to be 1×10⁻⁷ W/K, the temperature of the micro heater 173 is 1000 Kor more, so that the activation of the gettering thin film can besufficiently performed.

The material for the gettering thin film 185 is suitably selected fromalloys of Zr, Ti, or Zr, and Al, or a getter material of non-evaporationtype such as V (vanadium), for example. When the gettering thin filmadheres the gas in the micro vacuum package, and the gettering functionis degraded, the micro heater 173 is heated, and the temperature may beincreased up to a temperature (for example, 900 degrees) at which thegettering thin film 185 can activate again. By such heating, moleculesof the gas adhered to the surface is diffused inside the gettering thinfilm 185, so that the getter material can be exposed to the surface ofthe gettering thin film 185 again (activation).

In order to activate the gettering thin film 185 in this way, it isnecessary to increase the temperature of the micro heater 173 up to aremarkably high level as compared with the operation time of theelectronic device. In order that such heating does not badly affect theelectronic circuit integrated on one and the same substrate 160, it isdesired that the micro heater 173 and the substrate 160 be thermallyinsulated. In this embodiment, the thermal conductance between thesubstrate and the micro heater is set to be a small value of about 10⁻⁷W/K, so that there arises almost no bad influence on the electroniccircuit. In the case where the value of the thermal conductance islarge, i.e., in the case where the thermal insulating is insufficient,it is necessary to dispose the electronic circuit in a position distantfrom the region in which the micro heater 173 is formed. Thus, theminiaturization of the electronic device may be disturbed.

The gettering thin film 185 is fabricated in the following way. As shownin FIG. 33, after the polysilicon layer (the first sacrificial layer)171 is formed, a thin film of a gettering material is deposited on thepolysilicon layer 171 by sputtering, for example. Next, the thin film ispatterned into a desired shape, by photolithography and etchingtechniques.

The step shown in FIG. 33 is performed between the step of FIG. 21 andthe step of FIG. 22. The succeeding steps are the same as those shown inFIGS. 22 to 31.

According to the electronic device of this embodiment, the getteringthin film 185 is disposed below the micro heater 173, so thatirradiation of infrared rays to the micro heater 173 is not blocked.

Moreover, in this embodiment, a cavity also exists below the getteringthin film 185, so that the gettering thin film 185 can be easilyinsulated thermally from the substrate.

As described above, in this embodiment, a heat absorbing and emittingportion for heating the inside of the micro vacuum package for thepurpose of detecting the vacuum level in the cavity 163′, a temperaturedetecting portion for performing temperature detection, and anactivating portion for heating the gettering thin film for the purposeof increasing the vacuum level are realized by one micro heater.Therefore, the production cost can be reduced, and improvement in thedegree of integration of elements can be attained.

The above-mentioned heat absorbing and emitting portion, temperaturedetecting portion, and activating portion may be formed as separateelements. Since the pressure can be measured by using an element forabsorbing heat, a heat absorbing and emitting portion may be disposed,instead of the heat absorbing and emitting portion. The heat absorbingand emitting portion can be formed by a Peltier element. By detectingthe temperature inside the micro vacuum package which varies inaccordance with the heat generation or heat absorption of the Peltierelement, the thermal conductance g_(A) is obtained. The vacuum level canbe obtained from the obtained g_(A).

In this embodiment, the heat absorbing and emitting portion, thetemperature detecting portion, and/or the activating portion aredisposed one by one in each vacuum package. Alternatively, a pluralnumber may be disposed in one vacuum package.

The cavity may be formed inside the substrate. By etching part of thesubstrate, a cavity is formed, so as to perform thermal insulationbetween the heat absorbing and emitting portion, the temperaturedetecting portion, and/or the activating portion, and the substrate.Such a configuration can be fabricated in the following way, forexample. Specifically, first, after an etch stop layer is formed on thesurface of the substrate, an etching hole is formed in the etch stoplayer. Next, part of the substrate is etched via the etching hole, and acavity is formed inside the substrate.

As the substrate, instead of the silicon substrate, an SOI substrate maybe used. When the SOI substrate is used, after an etching hole is formedin an oxide layer existing inside the substrate, part of the substratepositioned below the oxide layer may be removed via the etching hole,thereby forming a cavity.

Instead of the formation of the cavity, a porous material such as poroussilicon may be disposed, thereby attaining thermal insulation.

The heat absorbing and emitting portion, the temperature detectingportion, and/or the activating portion can be formed on the surface ofthe substrate. In such a case, it is necessary to adopt a temperaturerange and a layout which do not badly affect the electronic circuit onthe substrate, as described above. If the heat absorbing and emittingportion, the temperature detecting portion, and/or the activatingportion are positioned inside the micro vacuum package, they may beformed on an arbitrary face.

The heat absorbing and emitting portion, the temperature detectingportion, and/or the activating portion may be formed from a materialother than silicon. For example, they can be formed from a metal such asTi or Pt, a metal oxide such as TiO or VO_(x), or a semiconductor suchas SiGe. In the case where the semiconductor is used, a PN junction isformed in the semiconductor, and the temperature can be detected basedon the variation in a current or a voltage in forward direction.

The detection of temperature by the temperature detecting portion may beperformed by, other than the method based on the resistance variation, amethod utilizing a pyroelectric effect, a method utilizing a variationof dielectric constant caused in accordance with the temperaturevariation (a dielectric bolometer), a method utilizing a phenomenon inwhich a thermal electromotive force occurs in accordance with atemperature difference between a hot junction and a cold junction in athermopile in which a thermocouple or a plurality of thermocouples areconnected in series (Seebeck effect), or the like.

In the above-described respective embodiments, the vacuum level isdetected based on the temperature of the micro heater in a static state.In the case where the time required for changing the micro heater intothe static state is too long, because the thermal conductance of themicro heater is large, it is possible to detect the vacuum level base onthe temperature in a transient state.

EMBODIMENT 9

With reference to FIG. 34, a ninth embodiment according to the presentinvention will be described. The electronic device of this embodiment isa camera (an imaging device) provided with an infrared area sensor.

As shown in FIG. 34, the camera of this embodiment includes an opticalsystem 210 for introducing infrared rays emitted from an object into aninfrared detecting unit (FIG. 34 shows an example using a reflectiveoptical system, but a refracting system may be used), a substrate 230having a plurality of infrared sensor elements 220 sealed in microvacuum packages, each micro vacuum package including one or a pluralityof elements, a Peltier element 250 formed on a back face of thesubstrate 230 opposite to the face on which the infrared sensor elementsare formed, a signal processing circuit 60 for processing output signalsof the infrared sensor elements, an element driving circuit 270 forpulse-driving the infrared sensor elements, a temperature detection &Peltier element driving circuit 280 for detecting a surface temperatureof the substrate 230 and controlling the substrate temperature bydriving the Peltier element 250, and a blocking plate 290 forexamination for blocking the infrared rays incident on the opticalsystem during the measurement of the temperature. When the opticalsystem 210 is not the reflecting optical system, but the refractingoptical system is used for experiments, a lens is formed by silicon orgermanium which transmits infrared rays. However, it is difficult forsuch materials to transmit visible light. For this reason, it ispreferred that the reflecting optical system be used.

Next, with reference to FIG. 35, the configuration of an infrareddetecting unit is described.

In this embodiment, as shown in FIG. 35, infrared detecting unitsarranged on the substrate 230 are sealed in cap units, respectively. Onthe substrate 230, a cell array in which a number of cells A1 to E5 eachincluding a resistive element (a bolometer) 201 and a switchingtransistor 202 are arranged in a matrix is disposed. The size of onecell is about 40 μm to 50 μm, for example, but it is sufficient that thesize is 20 μm or more which is substantially twice as long as thewavelength of the infrared rays to be sensed.

FIG. 35 also shows the signal processing circuit 260 for processingoutput signals of the infrared detecting units, the element drivingcircuit 270 for pulse-driving the infrared detecting units, and thetemperature detection & Peltier element driving circuit 80. The Peltierelement is an element utilizing a heat absorbing function in conjunctionwith the movement of carriers passing through a Shottky contact portion.When the temperature is measured, infrared rays incident on the opticalsystem is blocked by the blocking plate 290 for examination shown inFIG. 34.

A gate electrode of the switching transistor 202 in each cell isconnected to selection lines SEL-1 to SEL-5 extending from a verticalscanning circuit 209 (V-SCAN). One end of the resistive element 201 ofeach cell is connected to power supply line 205. A source of theswitching transistor 202 is connected to data lines 204 a to 204 eextending via a reference resistance R which is grounded from one endthereof. The data lines 204 a to 204 e are connected to an outputamplifier 206 via switching transistors SWa to SWe, respectively. Togate electrodes of the respective switching transistors SWa to SWe,signal lines 207 a to 207 e extending from a horizontal scanning circuit208 (H-SCAN) are connected.

Although not shown in FIG. 35, on a back face of the substrate, thePeltier element 250 to which the temperature detection & Peltier elementdriving circuit 80 is connected is disposed, thereby controlling thetemperature of the substrate 230.

The external vertical scanning circuit 209 (V-SCAN) and the horizontalscanning circuit 208 (H-SCAN) are connected to the external elementdriving circuit 270, thereby driving the infrared detecting units.Signals from the infrared detecting units are output to the signalprocessing circuit 260 via the output amplifier 206.

The infrared detecting unit includes a folding-type resistive element (abolometer) 201 disposed on the substrate 230, and a switching transistor202 for turning on or off a current to the resistive element 201. Thematerial of the resistive element 201 may be Ti, TiO, or polysilicon,and any one of them can be used. The switching transistor 202 includes asource region, a drain region, and a gate electrode, and electricallyconnects the resistive element 201 which is sealed in a vacuum conditionto an external circuit.

(Vacuum Level in the Micro Vacuum Package of the Infrared DetectingUnit)

In order that each infrared detecting unit operates with good accuracy,the vacuum level of the space in which the infrared detecting unit issealed is important. FIG. 36 is a graph showing the relationship betweenthe sensitivity of the infrared detecting unit and the vacuum level ofthe atmosphere.

As shown in FIG. 36, the sensitivity of the infrared detecting unit inthe atmosphere having a vacuum level of which the pressure is much morereduced from the vacuum level of about 1.0×10⁻² Torr (1.3 Pa) isimproved about ten times as much as the sensitivity of the infraredsensor at the atmospheric pressure. That is, when the pressure of theatmosphere of the region in which the infrared sensor is formed isreduced from about 10⁻² Torr (1.3 Pa), it is possible to realize aninfrared sensor having the sensitivity which is 10 times as high as thesensitivity of an infrared sensor which is driven at the atmosphericpressure. Therefore, when the infrared detecting unit can be sealed atthe vacuum level higher than the vacuum level of 10⁻² Torr (1.3 Pa), andthe vacuum level can be maintained after the sealing, a device with highsensitivity can be realized.

(Method for Determining the Vacuum Level)

After the temperature of the resistive element is increased by heatgeneration, and after the resistive element is left for a predeterminedperiod of time, the temperature of the resistive element is loweredagain, and becomes closer to the initial temperature. By detecting thechange in the temperature, the pressure can be measured.

FIG. 37 is a view for illustrating the movement in and out of the heatof the resistive element.

When the amount of heat generation of the micro heater is P₀, thethermal capacity of the resistive element is C, the change intemperature is ΔT, the thermal conductance of the micro heatersupporting portion is G₁, the thermal conductance of the atmospheric gasof the resistive element is G₂, and the frequency is ω, the followingrelationship expression is established.Cd(ΔT)/dt+(G ₁(ΔT)+G ₂(ΔT))=P _(o) e×p(jωt)

When the change in temperature ΔT is obtained from the above expression,the following expression is obtained.ΔT=P _(o) e×p(jωt)/((G ₁ +G ₂)+jωC)

When the resistive element is self-heated, the temperature T of theinfrared detecting unit is increased in proportion to the amount ofgenerated heat P_(o). In accordance with the increase in temperature T,the electric resistance R of the resistive element is changed.

FIG. 38 shows the change in temperature of the resistive element afterthe resistive element is self heated, and then left for a predeterminedperiod of time. In the figure, Pro1 to 3 denote temperature profiles ofelements 1 to 3 disposed in micro packages of different vacuum levels.

A static-state temperature period (I) is a period before the microheater is heated, and a heating period (II) is a period in which acurrent is caused to flow to the resistive element for heating. Thetemperature T of the resistive element is increased by 100 to 01° C.,for example, in the heating period (II). After the heating period (II)elapses, when the current flowing to the resistive element is stopped,the self-heating of the resistive element is stopped. Thus, thetemperature of the resistive element lowers. The rate of temperaturereduction is different depending on the thermal capacity C of theresistive element and the thermal conductance (G₁+G₂). For apredetermined heat retention period (III) which is previously set, thetemperature T of the resistive element lowers up to a temperaturecorresponding to the vacuum level.

In the example of FIG. 38, the temperature of the element 3 after theheat retention period (III) is higher than a threshold value (a settemperature), but the temperatures of the other elements 1 and 2 arelower than the threshold value. A difference between the temperature atthe start of the heat retention period and the temperature after theheat retention period is ΔT.

Based on the change in temperature ΔT of the resistive element, thevacuum level can be evaluated. Specifically, ΔT in each resistiveelement is measured, and an average of values excluding the maximumvalue and the minimum value among the measured values of ΔT. Then, bymedian filtering in which the average value is used as a threshold value(a set temperature), the vacuum level can be determined. By this method,in an electronic device in which the vacuum levels are reduced in anumber of vacuum packages with time, relative evaluation of vacuum levelin individual vacuum packages can be appropriately performed. Instead ofthe adoption of this method, a temperature corresponding to the vacuumlevel to be noted may be determined as a threshold value (a settemperature).

Hereinafter, with reference to FIGS. 35 to 39, a method of measuring atemperature T of a resistive element is more concretely described.

FIG. 39 is a timing chart for measuring the temperature of the resistiveelement in this embodiment. In FIG. 39, the abscissa indicates a time,and the ordinate indicates a driving voltage. Hereinafter, forsimplicity, the case where the temperatures of the resistive elements inthe infrared detecting units A1, B1, and C1 in FIG. 35 are detected isdescribed. A horizontal period is a period between HD clocks, and aframe is a period between VD clocks.

In the electronic device of this embodiment, when the vacuum level is tobe performed, the irradiation of infrared rays into the infrareddetecting units is blocked. More preferably, during several frames toseveral tens of frames before the static-state temperature condition (I)shown in FIG. 39, a condition in which line selection is not performedis maintained, so that the temperatures of the respective infrareddetecting units A1, B1, . . . are stabilized to constant levels.

Next, in the static-state temperature period (I), while the temperaturesof the respective infrared detecting units are maintained to beconstant, the vertical scanning circuit 209 (V-SCAN) is driven in acondition where a voltage of 5 V is applied to Vdd. The voltage isapplied to SEL#1, SEL#2, . . . , in this order. When the voltage isapplied to SEL#1, output signals Sco (first signal outputs) of therespective infrared detecting units A1, B1, C1, . . . are sequentiallyread out. The values of the output signals Sco are written into apreceding frame memory in the signal processing circuit 60 in the orderselected by the horizontal scanning circuit 208 (H-SCAN).

In the heating period (II), the vertical scanning circuit 209 (V-SCAN)is driven in a condition where a voltage of 25 V is applied to Vdd. Atthis time, the value of the voltage applied to Vdd is preferably largerthan the voltage applied in the static state (I) by 20 V or more. Whenthe vertical scanning circuit 209 (V-SCAN) is driven, SEL#1, SEL#2, . .. are selected in this order. When SEL#1 is selected, the voltage isapplied to the respective infrared detecting units A1, B1, C1. At thistime, since the resistance values of the infrared detecting units A1,B1, C1, . . . are substantially the same, the resistive elements in theinfrared detecting units A1, B1, C1, . . . reach substantially the sametemperature due to self-heating. In FIG. 39, the heating period includesthree horizontal periods. Alternatively, the heating may be extended byseveral tens of frames.

In the heat retention period (III), the vertical scanning circuit 209(V-SCAN) is driven in a condition where a voltage of 5 V is appliedagain to Vdd. The voltage is applied to SEL#1, SEL#2, . . . in thisorder. When SEL#1 is selected, output signals Sre of the respectiveinfrared detecting units A1, B1, C1, . . . are sequentially read out.The values of the output signals Sre (second signal outputs) are readout in the order selected by the horizontal scanning circuit 208(H-SCAN). In the signal processing circuit 60, the values of the outputsignals Sre after the heating period are compared with the values of theoutput signals Sco before the heating period stored in the precedingframe memory. Thus, temperature changes of the respective infrareddetecting units can be detected.

As described above, when output signals after a predetermined timeelapses after the heating of the resistive elements are read out, asdescribed above, the temperature of an infrared detecting unit in whichthe vacuum level is deteriorated is lower than the temperature of aninfrared detecting unit having a high vacuum level. Accordingly, bymeasuring the temperature change value before and after the heating, thevacuum level of the cap unit for sealing each infrared detecting unitcan be evaluated.

Hereinafter, the relationship between a temperature change value beforeand after heating and an output signal as a voltage signal which isactually output is described by way of an example of the infrareddetecting unit A1.

An output voltage V(A1) of the infrared detecting unit A1 is a productof a division resistance value of a resistance value R (A1) of theinfrared detecting unit A1 with the resistance value R(ref) of areference resistance R shown in FIG. 35, and a voltage Vdd applied tothe power supply line 205, as is seen from FIG. 35. Thus, the outputvoltage V(A1) of the infrared detecting unit A1 is represented by thefollowing expression.V(A1)={R(ref)/(R(A1)+R(ref))}·Vdd

On the other hand, a temperature T(t) of the infrared detecting unit A1is represented by the following expression.T(t)∝{R(A1)/(R(A1)+R(ref))}·Vdd∝Vdd−V(A1)

At this time, in the infrared detecting unit A1, a temperature changevalue ΔT from the temperature T(t0) in the static-state temperatureperiod (I) to the temperature T(t1) in the heat retention period (III)is represented by the following expression.ΔT=T(t1)−T(t0)

When the output voltage V(A1) is calculated, since the values of theresistance value R(A1) and the applied voltage Vdd are known, thetemperature change value ΔT can be uniquely determined depending on theoutput voltage V(A1) of the infrared detecting unit A1.

When the temperature of the Peltier element is set to be lower than anordinary temperature (10° C. or less, for example) by using thetemperature detection & Peltier element driving circuit 80, radiationheat from a tubular wall of the cap unit as the cap unit to thebolometer, so that the bolometer is cooled.

In FIG. 39, in the heating period (II), in order to match the timingsfrom the start to the readout for respective lines, the timings of startis shifted for SEL#1, SEL#2, and SEL#3. Alternatively, they may bestarted at the same time.

In the heating period (II) shown in FIG. 39, as a method of self-heatingthe bolometer, a voltage is applied to the bolometer. As another method,in the heating period (II), only the temperature of the Peltier elementis increased so as to heat the substrate without applying any voltage tothe bolometer. The temperature of the bolometer is increased by heatradiation from the substrate or the tubular wall of the cap unit. In thesucceeding readout period, the temperature of the Peltier element isreturned to the initial state (10° C., for example), and the readout isperformed for each line. In this method, the vacuum level is judged tobe worse, as the change in temperature of the bolometer is larger beforeand after the heating by the Peltier element. If a difference betweenthe detected temperatures is small, the vacuum level is judged to begood.

In the heating period (II) shown in FIG. 39, the heating may beperformed by using a combination of the bolometer and the Peltierelement.

(Signal Processing Method)

Next, a method for processing the output signals Sco and Sre obtained bythe measuring method shown in FIG. 39 in the signal processing circuit60 will be described with reference to FIG. 40. FIG. 40 is a diagramshowing a circuit for processing the output signals from the infrareddetecting units and complementing a defect in the measurement oftemperature for determining the vacuum level.

As shown in FIG. 40, in the measurement of temperature, an output signalSco output from an infrared detecting unit in the static-statetemperature period (I) as shown in FIG. 39 is AD-converted into adigital signal Dco in an ADC 66 of the signal processing circuit 60.Thereafter the digital signal Dco is stored in the preceding framememory 64.

Next, after the heating period (II), an output signal Sre output fromthe infrared detecting unit 20 which is left for a predetermined periodis also AD-converted into a digital signal Dre in the ADC 66 of thesignal processing circuit 60. Thereafter, in an output signal differencedetector 65 a, a signal indicating a difference between the value of thedigital signal Dco before the heating period and the value of thedigital signal Dre after the heating stored in the preceding framememory 64 is generated.

Moreover, in a defect detector 65 b, the output signal indicating thechange value is compared with a threshold value (a set voltage value)which is set based on the threshold value (the set temperature) shown inFIG. 38, thereby determining the vacuum level of the infrared detectingunit.

The position of the infrared detecting unit of which the vacuum level isdetermined to be deteriorated as the result of the determination of thevacuum level in the above-described way is stored into a defect positionmemory 63.

(Method of Complementing a Defect Pixel)

Next, a method of complementing an infrared detecting unit having adefect when the electronic device of this embodiment is used for acamera will be described with reference to FIG. 40.

When the camera using infrared detecting units is actually used,infrared rays emitted from an object are incident on the infrareddetecting units 20 in a condition where the blocking plate for test isnot used, so as to image output signals of the infrared detecting units20. When the process is repeated, the vacuum level is graduallydeteriorated in the region in which the respective infrared detectingunits 20 are sealed. The degree of deterioration is varied for each ofthe cap units in which the respective infrared detecting units 20 aresealed. Therefore, in some of the infrared detecting units 20, thesensitivity is deteriorated because of the serious deterioration of thevacuum level. The position of the infrared detecting unit can be knownby the above-described temperature measuring method.

When the camera is actually used, the infrared rays incident on theoptical system 10 are made into an output signal S via the infrareddetecting unit. The output signal S is input into an image processor 61of the signal processing circuit 60, and converted into a digital signalof 8 bits or more by the ADC 66. Thereafter, the digital signal is inputinto line memories Line Memory 1 to 3 of 3 lines or more by amultiplexer Mux67, and temporarily stored as a signal corresponding to apixel in each line (SEL#1, SEL#2, . . . in FIG. 35). The signals of thepixels in each line are input into the complementing processor 68. Inthe processor, a signal of a defective pixel stored in the defectposition memory 63 is subjected to interpolation complementingprocessing by utilizing signals of 8 pixels surrounding the signal ofthe defective pixel. Specifically, the complementing processing isperformed in such a manner that a signal of a pixel obtained by addingsignals of 8 pixels as the surrounding pixels (A1, B1, C1, A2, C2, A3,B3, C3 shown in FIG. 40), and multiplying ⅛ is substituted for thesignal of the pixel which is determined to be a defective pixel (B2shown in FIG. 40) based on the information from the defect positionmemory 63. Data after the complementing processing is input into ademultiplexer De# Mux69, so as to select a line required for thereadout. The line is output as the output signal to the external.

(Arrangement of Micro Vacuum Packages)

Hereinafter, the arrangement of the micro vacuum packages in thisembodiment will be described with reference to FIG. 41. FIG. 41 is adiagram schematically showing the arrangement of the micro vacuumpackages in the cell array shown in FIG. 35.

As shown in FIG. 41, in the cell array of this embodiment, micropackages A, micro vacuum packages B, and micro vacuum packages C arearranged. The micro vacuum packages A are formed from Si which transmitsinfrared rays, and a reduced pressure atmosphere is realized in themicro vacuum packages A without blocking the infrared rays. The microvacuum packages B are formed by sputtering Al which blocks infrared raysonto the surface thereof, and a reduced pressure atmosphere is realizedin the micro vacuum packages B with blocking the infrared rays. Themicro vacuum packages C are formed from Si which transmits infraredrays. Since an opening is formed in part thereof, an ambient pressureatmosphere is realized in the micro vacuum packages C without blockingthe infrared rays.

Hereinafter, functions of the respective micro vacuum packages and theinfrared detecting units sealed in the micro vacuum packages will bedescribed.

Infrared detecting units sealed by the micro vacuum packages A(hereinafter referred to as infrared detecting units A) are in thereduced pressure atmosphere, and in a condition where infrared rays areincident. By sensing infrared rays emitted from an object, the infrareddetecting units A output output signals in accordance with the intensityof the infrared rays from the object. The output signals include anoffset value which exists in a condition where any infrared rays are notincident. The vacuum level in the micro vacuum packages A is held at areference value or more at the time of sealing. Thereafter, it isconsidered that the vacuum level is gradually deteriorated with time anddue to the use of the device.

Infrared detecting units sealed by the micro vacuum packages B(hereinafter referred to as infrared, detecting units B) are in areduced pressure atmosphere which is substantially at the same level asthat of the infrared detecting units A, and in a condition where anyinfrared rays are not incident. Therefore, in the region in which theinfrared detecting units B are formed when the camera is actually used,it is possible to obtain outputs in a dark condition in which anyinfrared rays are not incident. By using the measured value, it ispossible to remove the offset value included in the output signals ofthe infrared sensors A.

Infrared detecting units sealed by the micro vacuum packages C(hereinafter referred to as infrared detecting units C) are in anambient pressure atmosphere. Therefore, when an examination fordetermining the vacuum level is performed, it is possible to know thetemperature of the infrared detecting units C in the ambient pressureatmosphere which is similar to the case where the vacuum level is mostdeteriorated. By comparing the temperature of the infrared detectingunits C with an average value of the temperatures in the infrareddetecting units A, it is judged how the deterioration progresses as awhole of the cell array.

In this embodiment, the micro vacuum packages B and the micro vacuumpackages C are disposed on the infrared detecting units positioned in aperipheral portion among the infrared detecting units which constitutethe cell array. In the present invention, the arrangement of the microvacuum packages B and the micro vacuum packages C is not limited tothis.

Specifically, if one micro vacuum package C is disposed for each line,the above-described effect can be attained. It is preferred that themicro vacuum packages B are disposed at the rate of about 20 to 30pixels for the cell array including signals of 510 pixels in ahorizontal direction.

In the cell array of the present invention, the micro vacuum packages Band the micro vacuum packages C are not necessarily formed. One of thetwo may be formed, or neither of them is formed.

In this embodiment, the micro vacuum packages C may not be formed forthe infrared detecting units C. In such a case, for the examination, theinfrared detecting units C are exposed to the ambient pressureatmosphere, and a difference between the self-heating and the heatdissipation of the bolometer can be measured. In this embodiment, themicro vacuum packages C each having an opening are formed for theinfrared detecting units C, for the purpose of performing more accuratemeasurement by making the conditions such as heat convection in theexamination closer to those of the infrared detecting units A and B.

The above-described temperature change measurement and the determinationof the vacuum level may be performed during the production or at theshipping, or may be performed by a user after the shipping. They will bedescribed below.

In the production, for example, micro vacuum packages A to C having thevacuum level of 3×10⁻³ Pa are formed. The forming method is performedsimilarly to the method performed in other embodiments. Specifically, astep of forming an etching hole, a step of forming a cavity by etching,and a step of closing the etching hole by sputtering may be performed.

A slit-like opening is formed in the micro vacuum package C, so that thevacuum level which is known in a vacuum chamber is held in the microvacuum package C. Therefore, in the case where temperature changemeasurement is performed at this time, the temperature change value ofthe infrared detecting unit C in the micro vacuum package C can be usedas a temperature change value corresponding to the vacuum level of theknown value and the optimum value. The corresponding relationship can beused for setting a threshold value.

Next, the determination of vacuum level at the shipping can be performedby detecting a micro vacuum package in which the vacuum level isdeteriorated due to bond failure of a cap in the production. Thedetermination of vacuum level after the shipping of the device isperformed for detecting a micro vacuum package in which the vacuum levelis deteriorated with time or as the use of the device. In thedetermination of vacuum level, a threshold value which is calculated byusing the corresponding relationship in the production may be previouslydetermined. Alternatively, a threshold value may be set by regarding anaverage value of the measured results of the temperature change value ofthe infrared detecting units C in the micro vacuum packages C as areference under an ambient pressure when the vacuum level is to bedetermined.

In this embodiment, one infrared detecting unit is disposed in one microvacuum package. Alternatively, a plurality of infrared detecting unitsmay be formed in one micro vacuum package.

In this embodiment, a bolometer is used as an element which requires thereduced pressure atmosphere. Other than the bolometer, a thermoelectricconversion element such as a PN diode, an electron releasing element, anelement for detecting or releasing a tera-wave having a wavelength of 40to 50 μm, and the like may be used. The electronic device of the presentinvention can be suitable for, other than the camera, various types ofinfrared sensors or other devices.

As the method of determining the vacuum level, a method of measuring atemperature after the device is left for a predetermined period of timeafter the heating period is described. Alternatively, in the presentinvention, a time required for reaching a predetermined temperatureafter the heating period is measured, and the time is compared with athreshold value (a set time), thereby performing the determination ofvacuum level.

In this embodiment, the vacuum level is sensed by using the currentvariation and the temperature variation. Alternatively, in theabove-described embodiments, the vacuum level can be sensed in a staticstate.

In Embodiments 7 and 8, a plurality of infrared detecting units andvisible-light detecting units are arranged at regular intervals on oneand the same substrate. Alternatively, the number of the infrareddetecting unit on the substrate may be one. An electronic device havingsuch a configuration is suitably used as a surveillance camera, forexample. According to such an electronic device which is used as asurveillance camera, when an existence of a person is sensed by theinfrared detecting unit, the imaging by the visible-light detecting unitis performed, so that the obtained image can be checked by a manager ofthe surveillance camera.

An example of an electronic device in which infrared detecting units andvisible-light detecting units are disposed on one and the same substrateis disclosed in Japanese Laid-Open Patent Publication No. 2003-17672,for example. The present invention can be widely applied to theelectronic device disclosed in the document.

INDUSTRIAL APPLICABILITY

According to the present invention, in the case where part of anelectronic device is disposed in a cavity, an etching hole disposed in acavity-wall member is closed by sputtering a metal or the like, so thatthe pressure of the cavity can be held at a low pressure (a highvacuum). Thus it is possible to provide an electronic device with highperformance, such as an infrared sensor with high sensitivity.

Moreover, according to the present invention, since a pressure measuringelement and a gettering thin film are disposed inside a cavity such as amicro vacuum package, it is possible to measure the vacuum level insidethe individual micro vacuum package. In addition, by appropriatelyactivating the gettering thin film inside the cavity, it is possible tomaintain the vacuum level in the cavity high.

1. A method of fabricating an electronic device comprising the steps of:(a) preparing a substrate on which part of the electronic device isdisposed, and forming a sacrificial layer which covers the part of theelectronic device on a selected region of the substrate; (b) forming acavity-wall film which covers the sacrificial layer on the substrate;(c) forming at least one opening which runs through the cavity-wall filmand reaches the sacrificial layer in the cavity-wall film; (d)selectively etching at least part of the sacrificial layer via theopening, thereby forming a cavity surrounding the part of the electronicdevice; and (e) forming a sealing member for closing the opening bysputtering.
 2. The method of fabricating an electronic device of claim1, wherein in the step (e), the sealing member is formed by sputtering ametal.
 3. The method of fabricating an electronic device of claim 1,wherein in the step (e), the sealing member is formed by sputteringsilicon.
 4. The method of fabricating an electronic device of claim 1,wherein in the step (e), after a film for the sealing member isdeposited in the opening and on the cavity-wall film, a portion of thefilm for the sealing member positioned on an upper face of thecavity-wall film is removed, thereby leaving the sealing member in theopening.
 5. The method of fabricating an electronic device of claim 1,wherein in the step (e), the sputtering is performed in a directioninclined with respect to a direction perpendicular to a main face of thesubstrate.
 6. The method of fabricating an electronic device of claim 1,wherein in the step (c), an opening having a shape which is wider in anupper portion and is narrower in a lower portion is formed.
 7. Themethod of fabricating an electronic device of claim 1, wherein in thestep (b), a side opening which reaches a side face of the sacrificiallayer is additionally formed.
 8. The method of fabricating an electronicdevice of claim 1, wherein in the step (b), the opening is formed sothat the opening does not overlap the part of the electronic device asseen from the direction of the sputtering in the step (e).
 9. The methodof fabricating an electronic device of claim 1, wherein in the step (e),the sputtering is performed under a pressure of 10 Pa or less.
 10. Themethod of fabricating an electronic device of claim 9, wherein in thestep (e), the sputtering is performed under a pressure of 5 Pa or less.11. The method of fabricating an electronic device of claim 1, whereinin the step (a), the sacrificial layer is formed from a polysiliconfilm, and in the step (b), a silicon oxide film is formed as thecavity-wall film.
 12. The method of fabricating an electronic device ofclaim 1, wherein the part of the electronic device is a detecting unitof an infrared sensor, in the step (a), the sacrificial layer is formedfrom a polysilicon film, and in the step (b), a polysilicon film and asilicon oxide film enwrapping the polysilicon film are formed as thecavity-wall film.
 13. The method of fabricating an electronic device ofclaim 1, wherein in the step (a), the sacrificial layer is formed from asilicon oxide film, and in the step (b), a polysilicon film is formed asthe cavity-wall film.
 14. The method of fabricating an electronic deviceof claim 1, further comprising the step of, after the step (d) andbefore the step (e), depositing a film on an exposed surface of thesubstrate by CVD, thereby making the opening smaller.
 15. The method offabricating an electronic device of claim 1, further comprising the stepof, before the step (a), forming a detecting unit of an infrared sensoras the part of the electronic device, and a sacrificial layer for alower cavity embedding the side and the bottom side of the detectingunit, wherein in the step (d), the sacrificial layer and the sacrificiallayer for the lower cavity are removed.
 16. An electronic devicecomprising: a substrate; part of the electronic device disposed on thesubstrate; a cavity-wall member surrounding the part of the electronicdevice with a cavity interposed therebetween; and a sealing member forclosing an opening disposed in a ceiling portion of the cavity-wallmember, wherein the sealing member is formed by sputtering.
 17. Theelectronic device of claim 16, wherein the sealing member is constitutedby silicon.
 18. The electronic device of claim 16, wherein the sealingmember is constituted by a metal.
 19. The electronic device of claim 16,wherein a pressure in the cavity is 10 Pa or less.
 20. The electronicdevice of claim 16, wherein a pressure of the cavity is 5 Pa or less.21. The electronic device of claim 16, wherein the sealing member isconstituted by a metal.
 22. The electronic device of claim 16, whereinthe sealing member is constituted by an oxide film.
 23. The electronicdevice of claim 16, wherein the part of the electronic device is adetecting unit of an infrared sensor, and the cavity-wall member isconstituted by polysilicon and a silicon oxide film enwrapping thepolysilicon.
 24. The electronic device of claim 16, wherein the part ofthe electronic device is a detecting unit of an infrared sensor, and theside and the bottom side of the detecting unit are surrounded by a lowercavity.
 25. The electronic device of claim 16, wherein the opening doesnot overlap the part of the electronic device as seen from the directionof sputtering.
 26. An electronic device comprising: a substrate; part ofthe electronic device disposed on the substrate; a cavity-wall membersurrounding the part of the electronic device with a cavity interposedtherebetween; and a sealing member for closing an opening disposed in aceiling portion of the cavity-wall member, wherein the sealing member isformed from a thin film, and an internal pressure of the cavity is 10 Paor less.
 27. The electronic device of claim 26, wherein a gettering thinfilm is disposed inside the cavity.
 28. The electronic device of claim27, wherein at least part of the cavity exists below the gettering thinfilm.
 29. The electronic device of claim 27, comprising a micro heaterfor heating the gettering thin film.